Method, apparatus and system for concentrating solutions using evaporation

ABSTRACT

The present disclosure is directed at a system, apparatus and method for concentrating a solution. The system includes a humidification device and a solution flow path for flow of a solution to be concentrated to the humidification device. The humidification device includes humidification media to facilitate evaporation of liquid from the solution to be concentrated to gas as the solution to be concentrated passes through the humidification media thereby concentrating the solution. The method includes flowing a solution to be concentrated along a flow path to a humidification device including humidification media, flowing a gas through the humidification media, and flowing the solution to be concentrated through the humidification media. There is evaporation of liquid from the solution to the gas as the solution passes through the humidification media thereby concentrating the solution and producing a humidified gas. The solution to be concentrated may be salt water and the gas may be air.

TECHNICAL FIELD

The present disclosure is directed at a method, apparatus and system forconcentrating solutions. More specifically, the disclosure is directed amethod, apparatus and system for desalinating a saltwater solution usingevaporation.

BACKGROUND

Treatment of waste saltwater to reduce volume is becoming increasinglyimportant, particularly for mining, oil and gas, and inland desalinationsystems. Mines can produce tailings water, which is typically ponded.Oil and gas operations can produce saltwater with the hydrocarbonreserve or during processing. Desalination is being increasingly used inboth industries as regulations require treatment of impaired water.Desalination is also used in coastal regions to produce freshwater fromseawater, with the more saline brine reject returned to the ocean.Inland brackish water can be desalted, however there is often noconvenient way to dispose of the brine reject. Common brine rejectmanagement options include discharge to a sewer or the environment,ponding, deep well injection, or treatment to produce solid salt inconcentrators and crystallizers. The first two methods are becoming morechallenging due to tightening environmental regulations and cost.Concentrators and crystallizers are used to distil water and producesolids, which can then be land filled or put to secondary use, yet theysuffer from high capital and energy cost. Capital costs are high due tothe extensive use of alloyed steels and titanium required at theoperating temperatures and pressures. Energy costs are high due to theuse of large volume compressors, which on average consume 20 to 60 kWhof electrical-mechanical power per cubic meter treated. Steam vapourcompressors may be used, which consume higher quality steam in place ofmechanical power. The cost of brine management is largely proportionalto the volume of brine requiring treatment. It is therefore beneficialto devise a plant to treat saltwater to reduce volume and preferablyproduce solids. Consequently, there is a need for an alternative methodand apparatus for concentrating solutions, such as desalinatingsaltwater.

As saltwater solutions are concentrated, salts can precipitate and scaleon various process components. When scaling occurs, performance of thesystem can quickly diminish. The most common reoccurring maintenancerequired in any humidification driven saltwater concentrating system isde-scaling the system components. Therefore, there is also a need todevise a system that efficiently and periodically removes scaling.

SUMMARY

According to a first aspect, there is provided a system forconcentrating a solution including a humidification device and asolution flow path for flow of a solution to be concentrated to thehumidification device. The humidification device includes humidificationmedia to facilitate evaporation of liquid from the solution to beconcentrated to gas as the solution to be concentrated passes throughthe humidification media thereby concentrating the solution.

The system may include a heater operable to heat the solution to beconcentrated to a temperature such that evaporation of liquid from thesolution to the gas occurs in the humidification media. The system mayalso include a gas flow generator for generating gas flow through thehumidification media. The gas flow generator may be at least one fan. Apump may be included in the solution flow path operable to pump thesolution to be concentrated to the humidification device. Thehumidification device may include a solution distribution header fordistributing the solution to be concentrated onto the humidificationmedia.

The system may include a solution container for the solution to beconcentrated. The solution flow path connects the solution containerwith the humidification device. The solution container may also be influid communication with an outlet of the humidification device suchthat the concentrated solution passes into the solution container.Alternatively, a separate collection container may be included forcollection of concentrated solution from the humidification device. Thesolution container or the collection container may include a bodyportion and a cone shaped portion configured to funnel the concentratedsolution into a solids precipitation area. The solution container or thecollection container may also include an inlet for the concentratedsolution and a deflection plate positioned beneath the inlet and abovethe solids precipitation area, such that the concentrated solutionentering the solution container or the collection container is deflectedaway from solids precipitating in the solids precipitation area.

The system may include a solids collection assembly for collectingsolids precipitated in the solids precipitation area. The solidscollection assembly may include a motorized filter belt configured toreceive precipitated solids from the solids precipitation area. Thefilter belt includes a material with a plurality of pores therethrough,the plurality of pores sized to permit solution to pass through thematerial while capturing the precipitated solids on the filter belt.Alternatively, the solids collection assembly may be an auger assembly.The auger assembly includes an auger positioned within an auger housing,a motor for rotating the auger within the auger housing, an auger inletpositioned in the solids precipitation area to collect precipitatedsolids, and an auger outlet for releasing precipitated solids. The augeris inclined such that the auger outlet is positioned vertically higherthan the auger inlet. The auger assembly may also include an augercooling circuit whereby coolant is used to cool the precipitated solidspassing along the auger and is heated in the process. The auger coolingcircuit includes a coolant inlet, a coolant outlet, a coolant pump forcirculating the coolant from the coolant outlet to the coolant inlet,and a coolant heat exchanger for removing heat from the coolant beforethe coolant enters the coolant inlet. The auger assembly may alsoinclude a coolant refrigeration circuit for cooling the coolant beforeit enters the coolant inlet. The coolant refrigeration circuit includesan evaporator, a compressor, a condenser, and an expansion device. Thecoolant heat exchanger includes the evaporator configured to transferheat from the coolant to a refrigerant within the evaporator such thatthe refrigerant evaporates, the compressor is configured to compress theevaporated refrigerant, the condenser is configured to condense thecompressed refrigerant and transfer the heat of condensation of therefrigerant to the solution to be concentrated before the solution to beconcentrated enters the humidification device, and the expansion deviceis configured to expand the compressed refrigerant before therefrigerant enters the evaporator.

The system may include a dehumidification device in gas flowcommunication with the humidification device such that humidified gasflows from the humidification device to the dehumidification device. Thedehumidification device is operable to condense vapour from thehumidified gas. The heat of condensation of the vapour may betransferred to a heat recovery circuit. The heat recovery circuit mayinclude a heat recovery evaporator, a heat recovery compressor, a heatrecovery condenser, and heat recovery expansion device. Thedehumidification device includes the heat recovery evaporator configuredto transfer heat generated by condensing vapour from the humidified gasto a heat recovery refrigerant within the heat recovery evaporator suchthat the heat recovery refrigerant evaporates, the heat recoverycompressor is configured to compress the evaporated heat recoveryrefrigerant, the heat recovery condenser is configured to condense thecompressed heat recovery refrigerant and transfer the heat ofcondensation of the heat recovery refrigerant to the solution to beconcentrated before the solution to be concentrated enters thehumidification device, and the heat recovery expansion device isconfigured to expand the compressed heat recovery refrigerant before theheat recovery refrigerant enters the heat recovery evaporator. Thesystem may include a duct connecting a gas outlet from thedehumidification device with a gas inlet into the humidification device.The duct may include a closable outlet vent for controlled release ofdehumidified gas from the duct as required and a closable inlet vent forcontrolled input of external gas into the duct as required. The duct mayalso include an internal closable return vent for controlledrecirculation of the dehumidified gas through the duct as required andan internal closable inlet vent for controlled introduction of thedehumidified gas into the humidification device as required.

The system may include a cleaning circuit for flushing a cleaningsolution through at least part of the solution flow path. The cleaningcircuit includes a cleaning solution container for cleaning solution,and a closable outlet flow path fluidly connecting the cleaning solutioncontainer with the solution flow path for controllable flow of cleaningsolution from the cleaning solution container through at least part ofthe solution flow path. The outlet flow path may be closable by a oneway valve. The cleaning circuit may also include a closable return flowpath fluidly connecting the solution flow path with the cleaningsolution container for return flow of cleaning solution to the cleaningsolution container. The return flow path may be closable by a one wayvalve. The cleaning circuit may include a heater for heating thecleaning solution. The system may include one or more sensors forsensing process conditions of the system that indicate a build up ofsolids in the solution flow path to provide an indication that thecleaning circuit needs to be activated. The cleaning circuit may includea humidification media flow path from the cleaning solution container toa plurality of cleaning solution nozzles directed at the humidificationmedia for spraying cleaning solution onto the humidification media. Thehumidification media flow path may include a controllable pump forpumping the cleaning solution to the plurality of cleaning solutionnozzles when required.

According to another aspect, the system may include a first solutionconcentrating circuit and a second solution concentrating circuit. Thefirst solution concentrating circuit includes a first humidificationdevice including a first humidification media, a first dehumidificationdevice in gas flow communication with the first humidification device, afirst solution flow path for flow of a first solution to be concentratedto the first humidification device, the first humidification mediafacilitating evaporation of liquid from the first solution to beconcentrated to a first gas as the first solution to be concentratedpasses through the first humidification media thereby concentrating thefirst solution and producing a first humidified gas. The second solutionconcentrating circuit includes a second solution container, a secondhumidification device including a second humidification media, a secondsolution flow path for flow of a second solution to be concentrated tothe second humidification device, the second humidification mediafacilitating evaporation of liquid from the second solution to beconcentrated to a second gas as the second solution to be concentratedpasses through the second humidification media thereby concentrating thesecond solution and producing a second humidified gas. The firstdehumidification device includes a condensing heat exchanger in thesecond solution flow path such that the second solution to beconcentrated passes internal the condensing heat exchanger and is heatedby heat generated from condensation of vapour from the first humidifiedgas on the external surface of the condensing heat exchanger. Thecondensing heat exchanger heats the second solution to be concentratedbefore the second solution to be concentrated enters the secondhumidification device.

A first duct may connect a first gas outlet from the firstdehumidification device with a first gas inlet into the firsthumidification device. The first duct may include a first closableoutlet vent for controlled release of the first dehumidified gas fromthe first duct as required and a first closable inlet vent forcontrolled input of external gas into the first duct as required. Thefirst duct may also include a first internal closable return vent forcontrolled recirculation of the first dehumidified gas through the firstduct as required and a first internal closable inlet vent for controlledintroduction of the first dehumidified gas into the first humidificationdevice as required.

A second dehumidification device may be included in gas flowcommunication with the second humidification device, such that thesecond humidified gas flows from the second humidification device to thesecond dehumidification device. The second dehumidification device isoperable to condense vapour from the second humidified gas. A heatrecovery circuit may be included to recover heat of condensation fromthe second dehumidification device. The heat recovery circuit includes aheat recovery evaporator, a heat recovery compressor, a heat recoverycondenser and a heat recovery expansion device, and the seconddehumidification device includes the heat recovery evaporator configuredsuch that heat generated from condensation of vapour from the secondhumidified gas is transferred to a heat recovery refrigerant within theheat recovery evaporator to evaporate the heat recovery refrigerant, theheat recovery compressor is configured to compress the evaporated heatrecovery refrigerant, the heat recovery condenser is configured tocondense the compressed heat recovery refrigerant and transfer the heatof condensation of the heat recovery refrigerant to the first solutionto be concentrated before the first solution to be concentrated entersthe first humidification device, and the heat recovery expansion deviceis configured to expand the compressed heat recovery refrigerant beforethe heat recovery refrigerant enters the heat recovery evaporator. Asecond duct may connect a second gas outlet from the seconddehumidification device with a second gas inlet into the secondhumidification device. The second duct may include a second closableoutlet vent for controlled release of the second dehumidified gas fromthe second duct as required and a second closable inlet vent forcontrolled input of external gas into the second duct as required. Thesecond duct may also include a second internal closable return vent forcontrolled recirculation of the second dehumidified gas through thesecond duct as required and a second internal closable inlet vent forcontrolled introduction of the second dehumidified gas into the secondhumidification device as required.

The system may include one or more additional solution concentratingcircuits positioned between the first and second solution concentratingcircuits such that solution to be concentrated in an additional circuitis heated in a condensing heat exchanger of a dehumidification device ofan upstream solution concentrating circuit before the solution to beconcentrated enters a humidification device in the additional circuit.

According to another aspect, there is provided a method of concentratinga solution including flowing a solution to be concentrated along a flowpath to a humidification device including humidification media, flowinga gas through the humidification media, and flowing the solution to beconcentrated through the humidification media, such that there isevaporation of liquid from the solution to the gas as the solutionpasses through the humidification media thereby concentrating thesolution and producing a humidified gas. The solution to be concentratedmay be salt water and the gas may be air. The method may includeprecipitating solids from the concentrated solution and collecting theprecipitated solids.

The method may include heating the solution to be concentrated beforethe solution to be concentrated enters the humidification device. Thesolution to be concentrated may be heated to a temperature greater thanthe wet bulb temperature of the gas flowing through the humidificationmedia. The solution to be concentrated may be heated to a temperaturethat is at or below ambient temperature.

The method may include controlling the temperature of gas flowingthrough the humidification media. The temperature of gas flowing throughthe humidification media may be controlled by controlling the flow ofthe solution to be concentrated through the humidification media and/orcontrolling the flow of the gas through the humidification media.

The method may include periodically flushing cleaning solution throughat least part of the flow path to de-scale the flow path. The cleaningsolution may be flushed through at least part of the flow path at orafter system shutdown. The cleaning solution may be flushed through atleast part of the flow path during operation when increased pump load isdetected. The method may also include sensing process conditions usingone or more sensors and flushing cleaning solution through at least partof the flow path when the sensors indicate a build up of solids in thesolution flow path. The cleaning solution may be heated prior toentering the flow path. The method may also include periodicallyflushing cleaning solution through the humidification media to de-scalethe humidification media. The cleaning solution may be heated prior toflushing the humidification media.

The method may include flowing the humidified gas through adehumidification device in gas flow communication with thehumidification device and condensing vapour from the humidified gas inthe dehumidification device to produce a liquid and a dehumidified gas.The heat of condensation from the step of condensing vapour from thehumidified gas may be recovered and used for heating the solution to beconcentrated before the solution to be concentrated enters thehumidification device. The heat of condensation may be recovered bytransferring the heat of condensation from the step of condensing vapourfrom the humidified gas to a refrigerant within an evaporator toevaporate the refrigerant, compressing the evaporated refrigerant in acompressor, condensing the compressed refrigerant in a condenser andtransferring the heat of condensation of the refrigerant to the solutionto be concentrated, and expanding the compressed refrigerant in anexpansion device before the refrigerant enters the evaporator. Thetemperature difference between the condenser and the evaporator may beminimized within predefined allowable operating ranges. The compressormay be operated at a predefined minimum pressure difference across thecompressor. The method may include monitoring the temperature of thesolution to be concentrated and the condensing refrigerant in thecondenser, calculating a heat transfer coefficient from heat load (kW)divided by the product of temperature difference and heat exchangesurface area (deg C m2), and if there is an increase in heat transfercoefficient above a threshold then initiating flushing of the condenserwith cleaning solution. The method may include flowing the dehumidifiedgas released from the dehumidification device to the humidificationdevice through a duct connecting a gas outlet of the dehumidificationdevice with a gas inlet of the humidification device. The method mayfurther include controlling the temperature of the gas flowing throughthe humidification media by reducing or increasing discharge of thedehumidified gas from the duct by closing or opening at least oneclosable vent in the duct.

According to another aspect, the method may include flowing a firstsolution to be concentrated along a first flow path to a firsthumidification device including first humidification media; flowing afirst gas through the first humidification media; flowing the firstsolution to be concentrated through the first humidification media, suchthat there is evaporation of liquid from the first solution to the firstgas as the first solution passes through the first humidification mediathereby concentrating the first solution and producing first humidifiedgas; flowing the first humidified gas through a first dehumidificationdevice in gas flow communication with the first humidification device;flowing a second solution to be concentrated through a condensing heatexchanger in the first dehumidification device to a secondhumidification device including second humidification media, wherebyheat generated from condensation of vapour from the first humidified gason an external surface of the condensing heat exchanger is transferredto the second solution flowing through the condensing heat exchanger toheat the second solution before the second solution enters the secondhumidification device; flowing a second gas through the secondhumidification media; and flowing the second solution to be concentratedthrough the second humidification media, such that there is evaporationof liquid from the second solution to the second gas as the secondsolution passes through the second humidification media therebyconcentrating the second solution and producing second humidified gas.

The method may include flowing a first dehumidified gas released fromthe first dehumidification device to the first humidification devicethrough a first duct connecting a first gas outlet of the firstdehumidification device with a first gas inlet of the firsthumidification device. The method may further include controlling thetemperature of the first gas flowing through the first humidificationmedia by reducing or increasing discharge of the first dehumidified gasfrom the first duct by closing or opening at least one closable firstvent in the first duct.

The method may further include flowing the second humidified gas througha second dehumidification device in gas flow communication with thesecond humidification device and condensing vapour from the secondhumidified gas in the second dehumidification device to produce a secondliquid and a second dehumidified gas. Heat of condensation from the stepof condensing vapour from the humidified gas may be recovered and usedfor heating the first solution to be concentrated before the firstsolution to be concentrated enters the first humidification device.Recovering the heat of condensation may include transferring the heat ofcondensation from the step of condensing vapour from the secondhumidified gas to a refrigerant within an evaporator to evaporate therefrigerant, compressing the evaporated refrigerant in a compressor,condensing the compressed refrigerant in a condenser and transferringthe heat of condensation of the refrigerant to the first solution to beconcentrated, and expanding the compressed refrigerant in an expansiondevice before the refrigerant enters the evaporator. The temperaturedifference between the condenser and the evaporator may be minimizedwithin predefined allowable operating ranges. The compressor may beoperated at a predefined minimum pressure difference across thecompressor. The method may include monitoring the temperature of thefirst solution to be concentrated and the condensing refrigerant in thecondenser, calculating a heat transfer coefficient from heat load (kW)divided by the product of temperature difference and heat exchangesurface area (deg C m2), and if there is an increase in heat transfercoefficient above a threshold then initiating flushing of the condenserwith cleaning solution. The method may further include monitoring andcontrolling temperature difference between the temperature of the secondsolution flowing through the condensing heat exchanger and thetemperature of the refrigerant flowing through the evaporator. Themethod may include flowing the second dehumidified gas released from thesecond dehumidification device to the second humidification devicethrough a second duct connecting a second gas outlet of the seconddehumidification device with a second gas inlet of the secondhumidification device. The method may further include controlling thetemperature of the second gas flowing through the second humidificationmedia by reducing or increasing discharge of the second dehumidified gasfrom the second duct by closing or opening at least one closable secondvent in the second duct.

According to another aspect, there is provided an apparatus for use in asolution concentrating system. The apparatus includes a humidificationdevice including humidification media, the humidification mediafacilitating evaporation of liquid from a solution to a gas as thesolution passes through the humidification media thereby concentratingthe solution and producing a humidified gas; and a dehumidificationdevice in gas flow communication with the humidification device suchthat the humidified gas flows from the humidification device to thedehumidification device. The dehumidification device is operable tocondense vapour from the humidified gas.

The apparatus may further include a heat recovery circuit including anevaporator, a compressor, a condenser, and an expansion device. Thedehumidification device includes the evaporator configured to transferheat generated by condensing vapour from the humidified gas to arefrigerant within the evaporator such that the refrigerant evaporates,the compressor is configured to compress the evaporated refrigerant, thecondenser is configured to condense the compressed refrigerant andtransfer the heat of condensation of the refrigerant to the solutionbefore the solution enters the humidification device, and the expansiondevice is configured to expand the compressed refrigerant before therefrigerant enters the evaporator.

The apparatus may further include a duct connecting a gas outlet fromthe dehumidification device with a gas inlet into the humidificationdevice. The duct may include a closable outlet vent for controlledrelease of dehumidified gas from the duct as required and a closableinlet vent for controlled input of external gas into the duct asrequired. The duct may further include an internal closable return ventfor controlled recirculation of the dehumidified gas through the duct asrequired and an internal closable inlet vent for controlled introductionof the dehumidified gas into the humidification device as required.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate one or more exemplaryembodiments:

FIG. 1 is a schematic view of a solution concentration system accordingto an embodiment.

FIG. 2 is a schematic view of a heat recovery and condensed waterproduction solution concentrating system according to an embodiment.

FIG. 3 is a graph showing air dry bulb temperature versus humidity ratioat saturation.

FIG. 4 is a graph showing air dry bulb temperature versus change in heatinput required to evaporate 1 kg of water for open and closed systems.

FIG. 5 is a graph showing air dry bulb temperature versus change invapour capacity of air for open and closed systems.

FIG. 6 shows the graph of FIG. 5 zoomed in on a smaller Y-axis range forhigher resolution.

FIG. 7 is a schematic view of an adjustable closed loop solutionconcentrating system according to an embodiment.

FIG. 8 is a schematic view of a solution concentrating system with solidextractor apparatus according to an embodiment.

FIG. 9 is a schematic view of a solution concentrating system withautomated clean-in-place system according to an embodiment.

FIG. 10 is a schematic view of a solution concentrating system withmultiple air humidification-dehumidification (HDH) effects with heatrecovery and condensed water production according to an embodiment.

FIG. 11 is a schematic view of a condensed water production solutionconcentrating system according to an alternative embodiment.

FIG. 12 is a schematic view of a heat recovery and condensed waterproduction solution concentrating system according to an alternativeembodiment.

FIG. 13 is a schematic view of a solution concentrating system withmultiple air humidification-dehumidification (HDH) effects with heatrecovery and condensed water production according to an alternativeembodiment.

DETAILED DESCRIPTION

Directional terms such as “top”, “bottom”, “upwards”, “downwards”,“vertically” and “laterally” are used in the following description forthe purpose of providing relative reference only, and are not intendedto suggest any limitations on how any article is to be positioned duringuse, or to be mounted in an assembly or relative to an environment.

The embodiments described herein concentrate solutions and produce a lowvolume concentrated solution or solid discharge at a reduced cost andlower energy consumption. The embodiments are generally directed atconcentration of a salt solution to produce concentrated saltwaterand/or solid salt and desalinated water, however, any solution can beconcentrated using the methods and systems of the embodiments described.Liquid, such as water, is removed from the solution by evaporation togas; solids, such as salts, may be precipitated, collected and thenpurged from the system. The embodiments described herein are generallydirected to the gas being air, however other gases may be used, forexample methane, helium, hydrogen, or nitrogen with differing heatcapacities that will provided different thermal and capacityperformance. The system may operate near atmospheric pressure andtemperature, enabling construction of parts from plastics as opposed tomore expensive corrosion resistant steels. Materials of constructionsuch as polyethylene or polypropylene may be beneficially used for theirsmooth surfaces and reduced likelihood of solid adhesion. All surfacesare designed for smooth transitions to prevent solid accumulation increvices. The system is configured and temperature gradients controlledto prevent precipitation in detrimental locations while encouragingprecipitation in desired locations.

The embodiments described herein are directed at a system forconcentrating a solution. The system includes a humidification deviceand a solution flow path for flow of the solution to be concentrated tothe humidification device. The humidification device includeshumidification media, which is any media or packing that facilitatesevaporation of liquid from the solution to gas as the solution passesthrough the humidification media and may include, but is not limited to,cooling tower splash fill or film fill packing and may be constructedfrom corrosion and scale resistant materials such as polyvinyl chloride,polypropylene or polyethylene. The humidification device may be anevaporative tower, a cooling tower, or other device which facilitatesevaporation of liquid to gas as the solution passes through the device.The humidification device may be constructed from non-corrosivefibreglass shell, plastic packing materials such as polyvinyl chlorideor polyethylene, and alloyed steel or stainless steel hardware toprevent corrosion issues. The humidification device may include asolution distribution header for distributing solution to beconcentrated onto the humidification media.

The system may include a solution container for the solution to beconcentrated. The solution container may also be configured to receiveconcentrated solution from the humidification device. In alternativeembodiments, the solution to be concentrated may be feed directly intothe solution flow path or the solution flow path may be in fluidcommunication with a reservoir or pond of saltwater. The solution flowpath may include a heater, such as a heat exchanger, operable to heatthe solution to be concentrated to a temperature such that evaporationof liquid from the solution to the gas occurs in the humidificationmedia. The heater may heat the solution to be concentrated to atemperature that is greater than the wet bulb temperature of the gasflowing through the humidification media. The solution flow path mayinclude a pump operable to pump the solution to be concentrated to thehumidification device.

The system may also include a gas flow generator for generating gas flowthrough the humidification media. In the embodiments described herein,the gas flow generator is at least one fan, however in alternativeembodiments, other gas flow generators may be used, such as a blower orexhauster. The fan may be positioned in or adjacent the humidificationdevice. The system may include a “clean-in-place” system or cleaningcircuit to periodically wash and de-scale parts of the system, such asthe pump, heater and humidification media.

In one embodiment solids, such as salt, are harvested from a solidprecipitation area by periodically purging a mixture of solids andliquids through an actuated purge valve onto on a filter belt. Solidslarger than the belt pores accumulate on the belt, while smaller solidsand liquids pass through the belt to a collection basin below. Beltmovement is coordinated with purge valve actuation to complete threeoperations: drying time, dropping into a collection bin, and beltcleaning. In another embodiment, precipitated solids may be collectedusing an auger assembly. Optional crystallization seeds, such as calciumsulfate, may be injected into the system to provide a nucleation siteand encourage precipitation.

The embodiments described herein are also directed to a method ofconcentrating a solution including flowing a solution to be concentratedalong a flow path to a humidification device including humidificationmedia, flowing a gas through the humidification media, and flowing thesolution to be concentrated through the humidification media, such thatthere is evaporation of liquid from the solution to the gas as thesolution passes through the humidification media thereby concentratingthe solution and producing a humidified gas. The flow path may be influid communication with a solution container or reservoir containingthe solution to be concentrated or the solution to be concentrated maybe feed directly into the solution flow path. The embodiments describedherein are generally directed to concentrating a salt water solutionusing air flowing the humidification media, however, any solution can beconcentrated using the method and other gases may be used, for examplemethane, helium, hydrogen, or nitrogen with differing heat capacitiesthat will provided different thermal and capacity performance.

The method may also include heating the solution to be concentratedbefore the solution to be concentrated enters the humidification device.The solution to be concentrated may be heated to a temperature greaterthan the wet bulb temperature of the gas flowing through thehumidification media. For example, but not limited to, the solution tobe concentrated may be heated to a temperature that is at least 1 degC., or at least 2 deg C., or at least 3 deg C., or at least 4 deg C., orat least 5 deg C., or at least 6 deg C., or at least 7 deg C., or atleast 8 deg C., or at least 9 deg C., or at least 10 deg C. greater thanthe wet bulb temperature of the gas flowing through the humidificationmedia. In alternative embodiments, the solution to be concentrated maybe heated to a temperature that is between 1 deg C. and 15 deg C.greater than the wet bulb temperature of the gas flowing through thehumidification media or any range in between, for example, between 1 degC. and 10 deg C., between 5 deg C. and 10 deg C. or any temperature inbetween, such as 1 deg C., 2 deg C., 3 deg C., 4 deg C., 5 deg C., 6 degC., 7 deg C., 8 deg C., 9 deg C., 10 deg C., 11 deg C., 12 deg C., 13deg C., 14 deg C., 15 deg C.

Referring to FIG. 1, there is shown a solution concentration system 101,which consists of three sub-systems:

-   -   Solution concentrating circuit: removes water from the system        via evaporative tower 120 and associated parts;    -   Clean-in-place circuit: periodically de-scales and cleans main        pump 108, heat exchanger 110, and evaporative tower packing 124;    -   Solids harvesting circuit: separates solids from liquids using        filter belt 144 and associated parts.

The solution concentrating circuit accepts input solution to beconcentrated such as saltwater 102 from an upstream process into bulktank 104, mixing with the bulk salt solution 105. Bulk tank 104 mayinclude an optional heater element 106 supplied with heat source 190 towarm the bulk salt solution prior to pumping in order to reduce thelikelihood of precipitation in downstream process pipework. Bulk saltsolution 105 exits bulk tank 104 via a bulk tank outlet and passesthrough a normally open bulk tank valve 112. The bulk tank outlet may bepositioned at least 15 cm above the tank base to prevent egress ofsolids that may accumulate in the base of the tank. The clean-in-placetank valve 182 is normally closed. Main pump 108 pumps the salt solutionthrough heat exchanger 110. The main pump 108 may be designed to handlesome solids such as an open face impeller, however alternative pumps maybe used. Exemplar heat exchangers include polyethylene pipe-in-pipe ortitanium plate and frame. Low grade heat from heat source 190 is appliedto the hot side of the heat exchanger in order to warm the salt solutiontemperature higher than the wet bulb temperature of the air passingthrough evaporator tower 120. The warm salt solution passes through thenormally open evaporative tower input valve 109 prior to entering theevaporative tower packing distribution header 122. The clean-in-placerecirculation valve 186 and evaporative tower packing spray valve 184are normally closed.

Warm salt solution is released by evaporative tower packing distributionheader 122 and drips through the evaporative tower packing 124 whichmaximizes mass transfer of water to air. The salt solution then passesinto the smooth bottomed collection basin 126, which may have a smallretained volume to minimize heat loss of the retained solution toatmosphere. Fan 125 moves air through the evaporative tower packing 124.A demister 128 may be provided to remove carryover droplets from theair.

Water is removed from the salt solution as it passes through theevaporative tower, with the rate of evaporation roughly proportional tothe temperature difference between the inlet salt solution and wet bulbtemperature of the air. Vaporization of water cools the salt solution,as well as concentrates it. The cooled, concentrated salt solutionspasses into a collection cone tank 130 via conduit 132. A deflectionplate 134 may be mounted under, but a distance from, the exit of conduit132. The deflection plate 134 beneficially prevents disturbance of thesalt collecting in the base of the cone tank 130. If the salt solutionreaches saturation due to the removal of water and cooling, salts willform. Heavier salt particles fall to the base while the lower densityand less saturated solution rises and exits through conduit 136 toreturn to bulk tank 104. The system is designed for temperaturestratification and hydraulics such that salts form in the cooler,stiller, base of cone tank 130 while salt formation is substantiallyprevented in the warmer bulk tank 104.

Precipitation in cone tank 130 may be encouraged through addition ofcrystal seeds 103, such as calcium sulfate seeds, which providenucleation sites for salt crystal growth. The cone tank 130 isperiodically purged of the precipitated salts collecting in the bottom,along with some solution through actuated valve 140. Actuated valve 140may be a butterfly valve with a rubber seat for reliable operation,however ball or diaphragm valves or other valves could also be employed.An optional distributor 141 directs the exiting salt-solution mixture tofilter belt 144.

Filter belt 144 consists of a robust material with pore sizes smallenough to capture the salts in question but to also allow gravitydrainage of solution through to collection basin 150. The salt solutionin basin 150 can be pumped back to the bulk tank 104 using basin pump152. The collection basin 150 may include an optional heater element(not shown) to reduce the likelihood of precipitation in pump 152 andits associated pipework. Exemplar filter belts include, but are notlimited to, Clear Edge Filtration's PX60™ filter belt. Filter belt 144may optionally be supported with a series of rollers 147 and bearings.The rollers 147 may be plastic, for example HDPE, and the bearings maybe PTFE pillow block bearings. The belt may be moved by a drive system148 using exemplar silicon coated stainless steel rollers 143 to providetraction drive. The stainless steel rollers 143 are kept well away fromthe saltwater splash zone to prevent corrosion.

Filter belt movement may be timed and coordinated with the actuatedvalve 140 as follows:

-   -   1. Belt stationary during cone tank 130 purge and solution        gravity filtering;    -   2. Move belt using drive system 148 to drying zone 145 and stop;    -   3. During belt movement in step 2 solids collected in previous        purge and passed through the drying zone 145 are discharged from        the end of the belt 144 into collection bin 154, from where they        are subsequently disposed;    -   4. Also during belt movement in step 2 belt washer may be        initiated to spray the belt with clean-in-place solution 185 via        high pressure low flow nozzles 146, removing encrusted solids;        and    -   6. Purge cone tank 130 again after belt stop and repeat steps 2        to 4.

The system may include an optional shield 142 to prevent saltwatersplash-out. An exemplar shield 142 could be Plexiglas, providing thebenefits of corrosion resistance and transparency for operators totroubleshoot machine operation. The clean-in-place system may alsoinclude plumbing to optional nozzles spraying bearings or accumulationpoints. It is beneficial to minimize the volume of clean place solution185 sprayed in order to minimize the amount of water added to thesystem. The drying zone 145 may be exposed to ambient and solar energyin appropriately dry climates, or enclosed and equipped with forced airand/or heaters to assist drying.

In alternative embodiments (not shown) a filter press or centrifuge isutilized to separate solids and liquids in place of the filter beltsystem. A filter press or centrifuge would accept a solids-solutionmixture from valve 140, separate the solids for disposal, and return thesolution to the saltwater concentrating circuit via a pump similar inintent to basin pump 152.

The clean-in-place system periodically circulates clean-in-placesolution 185 through main pump 108 and heat exchanger 110 to de-scalethem. The clean-in-place system may also spray clean-in-place solution185 to clean belt 144 and evaporative tower packing 124. Theclean-in-place solution 185 may be fresh water due to its solubilityaction, but could also be saltwater or other solution. Theclean-in-place solution 185 may be heated with element 181 in tank 180via heat supply 190 in order to increase its de-scaling capability. Theclean-in-place solution 185 may have acid, base, or anti-scalants addedto increase de-scaling capability, depending on the composition of thesalt water being processed. If for example the salt water is high insilica, the pH of the clean-in-place solution 185 may be increased toencourage silica de-scaling, while if the salt water is high incarbonates, the pH of the clean-in-place solution 185 may be reduced.

Operation of the clean-in-place system may be based on one or more ofthe following criteria:

-   -   A timer set to predetermined operational needs;    -   Increase pump load or vibration;    -   Reduced heat transferred determined as decreased heat transfer        coefficient calculated through means known to those skilled in        the air based on thermal load and temperature differences        between the heat source 190 and saltwater being heated;    -   Increase evaporative tower fan 125 load indicating packing        scaling.

Pump and heat exchanger clean-in-place operation involves shutting downthe evaporation circuit by closing valves 112 and 109, and openingvalves 182 and 186, with valve 184 initially remaining closed. Thisaction will circulate the clean-in-place solution 185 through the mainpump 108 and heat exchanger 110, thereby providing some degree ofde-scaling as built-up salts re-dissolve into solution. Theclean-in-place solution 185 is circulated back to tank 180 until a setperiod of time has passed to allow for cleaning. Tower packing 124 canbe cleaned immediately after, or any time as required, by maintainingvalves 112 and 109 closed and 182 open, opening valve 184 and closingvalve 186; thereby diverting clean-in-place solution 185 to theevaporative tower packing cleaning spray nozzles 188. The evaporativetower packing cleaning spray nozzles 188 direct warm clean-in-placesolution 185 at a high pressure and low flow rate at the packing surfaceto remove attached scale. A minimal amount of water is beneficiallyadded to the system, since all water added needs to be subsequentlyremoved and as a result the addition of water decreases the plant's netwater processing capacity. Make-up clean-in-place solution 183 can beadded to the clean-in-place tank 180 optionally using an actuated valveor float valve. Valves 112, 182, 184, 186, and 109 may be automaticallyactuated in accordance with the above mentioned operation criteria andposition instructions through use of common air or electric valveactuation systems (not shown).

In the embodiment described above, which is open to atmosphere, thesolution concentrating circuit removes moisture by evaporation to airand thereby concentrates the salt solution. In order to maintainevaporation however, heat must be supplied. Without heat supply, thesystem will cool to the wet bulb temperature of the air and evaporationwill cease. The heat supplied need only be sufficient to warm the saltsolution to a temperature about 1 to 10 deg C. warmer than the wet bulbtemperature of the air. For example, at an ambient temperature of 30 degC. and relative humidity of 39%, the wet bulb temperature is 20 deg C.,therefore the salt solution need only be heated to 30 deg C. (nearambient) prior to entering the evaporative tower packing distributionheader 122. Although the quality of heat supplied is low, owing to itslow temperature, the quantity can be quite large due to the high latentheat of vaporization of water (approximately 2400 kJ/kg near 30 deg C.).In addition, the vapour evaporated from the salt solution representsnear-pure water lost from the system. It is therefore beneficial todevise a system that captures and recycles heat as well as condenseswater from evaporative tower warm moist air exhaust.

In an alternative embodiment a portion of the heat of vaporization lostduring evaporation to the atmosphere is recycled and used to heat thesolution to be concentrated before it enters the evaporative tower. Thisis achieved by ducting the warm, moist exhaust of the evaporative towerover a heat pump evaporator. The heat pump upgrades heat from condensingevaporative tower exhaust moisture to heat the evaporative tower feedsolution. Beneficially, low grade heat energy is reduced or removedcompletely, reducing the need for an external low grade heat source.

The heat pump will require higher grade mechanical energy to drive theheat pump compressor. However heat pumps provide a coefficient ofperformance (COP) effect, resulting in a COP multiple of units heatenergy upgraded per unit of mechanical energy used to drive the heatpump compressor. For example, with heat pump COP of three: three unitsof heat energy will be upgraded for each unit of mechanical energy inputto the heat pump compressor resulting in a total of four units of heatenergy being added to the saltwater (three units from the evaporator andone unit from the compressor). In sum, a smaller portion of high gradeenergy is used by the heat pump to recycle and upgrade heat content fromthe warm moist evaporative tower exhaust for re-input into the warmerevaporative tower input solution, thereby reducing or removing the needfor an external heat supply.

Referring to FIG. 2, there is shown a heat recovery and condensed waterproduction solution concentrating system 201, which includes threesub-systems:

-   -   Solution concentrating circuit: removes water from the system        via evaporative tower 220 and associated parts;    -   Heat pump circuit: captures heat from evaporative tower warm        moist air exhaust 229 and upgrades it to heat the solution        entering the evaporative tower 220;    -   Optional clean-in-place circuit: periodically de-scales and        cleans main pump 208, heat exchangers 210, 211 and evaporative        tower packing 224;

The solution concentrating circuit accepts make-up solution, such assaltwater 202, from an upstream process into bulk tank 204. Bulk tank204 may include an optional heater element 206 supplied with heat source290, which warms bulk salt solution 205 prior to pumping andbeneficially reduces the likelihood of precipitation in downstreamprocess pipework. Bulk salt solution 205 exits bulk tank 204 via anoutlet and passes through a normally open bulk tank valve 212. Theoutlet may be positioned at least 15 cm above the tank base to preventegress of solids that may accumulate in the base of the tank. Optionalclean-in-place tank valve 282 is normally closed. Main pump 208 pumpsthe salt solution 205 through a heat pump condenser heat exchanger 211and main heat exchanger 210.

The objective of both heat exchangers 210 and 211 is to warm the saltsolution temperature to approximately 5 deg C. higher than the wet bulbtemperature of the surrounding air, which will promote evaporation ofwater to atmosphere in evaporative tower 220 and thereby concentrate thesalt solution 205. The heat pump condenser heat exchanger 211beneficially reduces, or removes completely, the quantity of low gradeheat from heat source 290 that needs to be applied to the hot side ofthe main heat exchanger 210.

The warm salt solution exiting main heat exchanger 210 passes throughthe normally open evaporative tower input valve 209 prior to enteringthe evaporative tower packing distribution header 222. The optionalclean-in-place recirculation valve 286 and evaporative tower packingspray valve 284 are normally closed. The warm salt solution passesthrough the evaporative tower packing distribution header 222 and dripsthrough the evaporative tower packing 224 while fan 225 moves airthrough the evaporative tower packing, promoting mass transfer of waterto air. Evaporative tower inlet louvers 221 direct air into theevaporative tower packing and prevent splashing of saltwater out of theevaporative tower air inlet when the fan 225 is not on. Water evaporatesfrom the salt solution 205 to the air if the salt solution temperatureis higher than the wet bulb temperature of the air. As a result, warmmoist air exhaust 229 is produced while the salt solution 205 is cooledthrough loss of heat of vaporization and concentrated through loss ofwater. The cooled, concentrated salt solution collects in collectionbasin 226 and returns to the bulk tank 204 through conduit 223, whichmay include an optional strainer or filter (not shown) to remove anydebris. The evaporative tower 220 may be similar in construction to acooling tower; however the evaporative tower 220 may be constructed fromnon-corrosive fibreglass shell, plastic packing materials such aspolyvinyl chloride or polyethylene, and alloyed steel or stainless steelhardware to prevent corrosion issues.

The evaporative tower moist air exhaust 229 passes through todehumidifying device 260 under action of an optional fan 264. Fan 264may be optionally removed if evaporated tower fan 225 is sufficientlysized to induce the required air flow. The dehumidifying device 260includes a heat pump refrigerant evaporator 270. Inside the heat pumprefrigerant evaporator 270 refrigerant evaporates at a temperature lowerthan the wet bulb temperature of the air plus an additional margin toallow for heat transfer resistance. As a result, water vapour condensesfrom the evaporative tower moist air exhaust 229 in contact with theexternal surface of the heat pump refrigerant evaporator 270. As watervapour condenses, the latent heat of condensation is transferred to therefrigerant inside the heat pump refrigerant evaporator 270.

Low pressure refrigerant gas passes from the heat pump refrigerantevaporator 270 to heat pump compressor 274. Heat pump compressor 274compresses the refrigerant gas to a sufficient pressure that will enablecondensation of high pressure refrigerant gas in the heat pump condenserheat exchanger 211 at a temperature greater than the salt solution 205inside the heat exchanger 211. This results in condensation of therefrigerant inside the tubes of the heat pump condenser heat exchanger211. Condensed liquid refrigerant passes through an expansion device 278which lowers the pressure from the high to the low pressure side of theheat pump cycle allowing low pressure refrigerant to enter theevaporator. Condensing refrigerant in heat exchanger 211 transfers therefrigerant's latent heat of condensation to heat the salt solution 205before it enters the evaporative tower 220. Beneficially, the net resultis that the latent heat from the condensing exhaust moist air 229 incontact with refrigerant evaporator 270 is upgraded to a highertemperature and recycled to heat salt solution 205 before it enters theevaporative tower 220, thereby reducing or eliminating the system netheat input required from heat source 290 in the main heat exchanger 210while also producing condensed water vapour 266 that may be put to asecondary beneficial use. Condensed water vapour 266 is captured inbasin 267 and output from the plant through conduit 269.

Exemplar heat pump compressors include, but are not limited to, standardrefrigeration system piston or screw compressors sized to match the heatpumps' evaporator and condenser operating pressures and flow rates. Therefrigerant evaporator 270 is exposed to the moist air exhaust 229 whichis less corrosive than other heat transfer surfaces in the system thatare exposed to the salt solution 205, therefore, exemplar refrigerantevaporator 270 materials may be, coated copper, coated cupric-nickel,aluminum, or titanium. Exemplar coatings include heresite basedcorrosion inhibiting paints and epoxies. Exemplar refrigerants include,but are not limited to, R410A, R134a, or R245fa for heat pump cyclesoperating with a condensing temperature greater than 55 deg C. The heatpump condenser heat exchanger 211 is exposed to the corrosive saltsolution 205 and therefore should be designed for corrosion resistance.Exemplar heat exchangers 210, 211 include, but are not limited to,tube-in-tube polyethylene heat exchangers or titanium plate and frameheat exchangers. The heat pump circuit 272 may be loaded and unloaded,or cycled on or off, based on the availability of heat from heat source290, measured as the salt solution 205 temperature after valve 209.

The dehumidifying device 260 can include an optional demister 265 thatentrains any water droplets carried over to prevent loss to theenvironment. In an alternative embodiment (not shown), the air flow maybe orientated in vertical rather than horizontal configuration. Also theair flow in evaporative tower 220 may be oriented horizontally withvertical air flow in dehumidifying device 260, providing the benefit ofadditional demisting as condensed vapour droplets will tend to fall outof the air flow as it turns from a horizontal to a vertical path.

The optional clean-in-place system periodically circulatesclean-in-place solution 285 through main pump 208, main heat exchanger210 and heat pump condenser heat exchanger 211 to de-scale them, andsprays clean-in-place solution 285 to evaporative tower packing 224. Theclean-in-place solution 285 may be heated with element 281 in tank 280via heat supply 290. As previously discussed, the solution 285 may haveacid, base, or anti-scalants added to reduce scaling, depending on thecomposition of the salt solution 205. Initiation of the clean-in-placesystem may be based on one of the criteria discussed above in relationto FIG. 1.

Pump and heat exchanger clean-in-place operation involves shutting downthe evaporation circuit by closing valves 212 and 209, and openingvalves 282 and 286, with valve 284 initially remaining closed. Thisaction will circulate the warm clean-in-place solution 285 through themain pump 208 and heat exchangers 210, 211, thereby providing somedegree of de-scaling as built-up salts re-dissolve into solution. Theclean-in-place solution 285 is circulated back to tank 280 through valve286 until a set period of time has passed to allow for cleaning. Towerpacking can be cleaned immediately after, or any time as required, bymaintaining valves 212 and 209 closed and 282 open, opening valve 284,and closing valve 286; thereby diverting clean-in-place solution 285 tothe evaporative tower packing cleaning spray nozzles 288. Theevaporative tower packing cleaning spray nozzles 288 may direct warm lowsalinity water at a high pressure and low flow rate at the packingsurface 224 to remove attached scale. Preferably, a minimal amount ofwater will be added to the system. Make-up clean-in-place solution 283,which may be freshwater due to its increase solubility action, but couldalso be saltwater, can be added to the clean-in-place tank 280 based onan actuated valve or float valve. Valves 212, 282, 284, 286, and 209 maybe automatically actuated through use of common air or electric valveactuation systems.

The embodiment described above with reference to FIG. 2 is an openhumidification-dehumidification solution concentrating system. The opensystem described intakes outside air into the humidification zone anddischarges air from the dehumidification zone to the environment. Froman energy efficiency stand point, measured as units of mechanical powerconsumed by the heat pump compressor per unit of water processed, it isbeneficial to operate the heat pump with the heat pump evaporator 270temperature and refrigerant condensing heat exchanger 211 temperature asclose as possible, while heating the saltwater to above the wet bulbtemperature of the air but not above the ambient temperature whenentering distribution header 222. Maintaining the saltwater temperatureentering the evaporative tower at or below ambient will prevent sensibleheat loss to the air. Cold climates may limit the capacity of openhumidification-dehumidification systems. This is because cooler airholds less moisture. Therefore, a greater volume of colder than warmerair needs to be processed, making the footprint larger. Supplementaryheat may be provided to pre-heat air input to open systems, yet thisheat is rejected and lost.

Psychrometrics govern air's thermodynamic properties and their changeswith temperature and humidity. FIG. 3 is a plot of air dry bulbtemperature versus humidity ratio. Humidity ratio is a measure of air'svapour capacity, at a certain temperature, in terms of kg vapour per kgdry air at saturation, or 100% relative humidity. FIG. 3 shows thathumidity ratio increases with temperature. A greater rate of increaseoccurs at higher temperatures. This means that a 1 deg C. change intemperature at higher temperatures will result in a greater change inhumidity ratio. For example, saturated air at 30 deg C. can holdseventeen times more water vapour per kg dry air than saturated air at−10 deg C. Meaning the warmer system has a higher capacity to processwater mass for the same volumetric capacity. Air density allowsconversion to volume, but also changes with temperature. For example,air at 30 deg C. is 1.4 times less dense than air at −10 deg C., meaningthe warmer air will occupy 40% more volume than the cooler air. Dividinghumidity ratio (kg H2O/kg dry) by density (kg dry air/m3) gives vapourcapacity in terms of kg moisture held per m3 dry air (kg H2O/m3).Applying air density to the example, a system operating at 30 deg C.will have twelve times higher vapour capacity per unit volume (17divided by 1.4) than a system operating at −10 deg C. It can thereforebe beneficial for capacity, to operate a closed loop system at 30 deg C.as opposed to an open system with ambient air entering at −10 deg C.

A key difference between the open and closed system is that an opensystem can accept atmospheric air that is below saturation, for exampleat 75% relative humidity, whereas air in a closed system will always benear 100% relative humidity. Air that is below 100% relative humiditycan hold additional moisture at the same dry bulb temperature untilsaturation is reached. This reduces heat input.

Exemplar thermodynamic properties for air at 75% and 100% relativehumidity, and 30 and −10 deg C., are shown in Table 1 below. Forexample, 75% relative humidity air at 30 deg C. can accept an addition0.007 kg H20/kg dry air (0.0272-0.0202) as it moves towards 100%relative humidity. It could therefore be beneficial to operate an opensystem in warmer dryer climates were incoming air has additional vapourcapacity. In contrast, the colder −10 deg C. air can only accept 0.0004kg H20/kg dry air as it moves from 75% towards 100% relative humidity.

TABLE 1 Air dry bulb temperature versus humidity ratio at saturationHumidity Ratio Air Dry Bulb Relative Wet bulb (kg H2O/ Enthalpy (deg C.)Humidity (deg C.) kg dry air) (kJ/kg dry air) 30  75% 26.30 0.0202 81.7530 100% 30.00 0.0272 99.69 −10  75% −10.75 0.0012 −7.08 −10 100% −10.000.0016 −6.09

For air below saturation, which is possible in an open system, heatadded in the humidification zone is used largely for latent heatingpurposes (evaporating water) as opposed to sensible heating purposes(heating air). On the other hand closed systems operate with the airalways at saturation. Therefore, the only way to add water vapour tosaturated air is by heating the air to increase its vapour capacity. Airheating to increase vapour capacity can be achieved by direct contactwith the warmer humidifying solution or by heat exchange with anexternal heat source. In general, heating saturated air to evaporatewater will require more heat input than evaporating water to air that isbelow saturation. It is therefore more energy efficient to humidify airbelow saturation than to heat and humidify air already at saturation,making the heat load higher for closed systems.

FIGS. 4, 5 and 6 compare the thermal and capacity performance of closedand open systems.

FIG. 4 compares the heat input required for a one degree Celsius changein temperature for open and closed systems over a range of air dry bulbtemperatures on the x-axis. Heat input is expressed as kJ per kg ofwater vapour added to the air. FIG. 4 shows two scenarios as follows:

-   -   1. Closed loop: heating saturated air (100% relative humidity)        by 1 deg C., increasing vapour capacity, and evaporating water        until saturation is reached again.    -   2. Open system: taking in 75% relative humidity air and        humidifying it to 100% relative humidity.

FIG. 4 shows that closed systems have higher heat input requirementsthan open systems, yet the difference diminishes at higher temperatures.For example, at temperatures higher than 30 deg C. the heat inputrequirements for open and closed systems converge as they approach thelatent heat requirement to evaporate water. As a result, the additionalheat input requirement for closed systems becomes marginal attemperatures that are for example higher than 30 deg C. In turn makingclosed systems' thermodynamic performance comparable to open systems atthe same temperature. Therefore, operating a closed system at anelevated temperature in a cold climate can achieve the capacity benefitswith marginal heat load increase.

FIGS. 5 and 6 compare open and closed systems' change in vapour capacitywith temperature. FIGS. 5 and 6 show the change in vapour capacity (kgH2O per m3 dry) for the same two scenarios as given in FIG. 4. FIGS. 5and 6 are identical with the exception that FIG. 6 zooms in on a smallerY-axis range for higher resolution.

FIGS. 5 and 6 show that in an open system, humidifying air from 75% to100% relative humidity will result in greater vapour capacity increasethan heating saturated air by 1 deg C. This means at the sametemperature, a closed system will have a lower capacity than an opensystem. However, closed systems can be operated at an elevatedtemperature without the need to continuously pre-heat the air since warmexhaust air is re-circulated rather than discharged. FIGS. 5 and 6 alsoshow that a closed system operating at an elevated temperature can havea higher capacity than an open system at a cooler temperature. Forexample, a closed system at 30 deg C. heating saturated air by 1 deg C.has a change in vapour capacity of 0.0303 kg H2O per m3 dry air, whichis three and a half times higher than the change in vapour capacity ofan open system at −10 deg C. Therefore, in an exemplar −10 deg C. coldclimate, greater capacity will result from a closed system at 30 deg C.vs. an open system at −10 deg C., with little deficit in increased heatload according to FIG. 4. The capacity increase benefits of closedsystems become even more prevalent at operational temperatures of 40 or50 deg C.

If designed to operate at an elevated temperature, the closed systemcapacity can be maintained regardless of external environmenttemperatures. This removes capacity fluctuations with changes inweather, something that open systems suffer from unless air preheat isemployed. For example, an order of magnitude capacity decrease resultswhen an open system operating at 22 deg C. is operated at −10 deg C.This can result in upstream and downstream process managementchallenges. Beneficially, a closed system will not experience thesecapacity swings with external environment temperature if the internaltemperature can be maintained through sound insulation practices andreplacement of sensible heat losses to the external environment.

Most climates see temperature swings, between day and night as well asseasons. Closed systems may be preferred for their high capacity when itis cold outside. During warmer times open systems offer both lowerenergy and higher capacity as shown in FIGS. 5 and 6. It is thereforeadvantageous to develop a hybrid open-closed system that can operatefrom fully closed during colder times to fully open in warmer weather.The proportion of open vs. closed depends on the closed system designand capacity needs of the operator. In reference to FIGS. 5 and 6,drawing a horizontal line from a selected closed system elevatedoperating temperature to intersect the open system curve reveals thetemperature on the x-axis under which closed systems will have highercapacity than open systems. For example, at a 30 deg C. elevatedoperating closed system temperature will have higher capacity than opensystems if the external environment is less than 4 deg C. Above 4 deg C.and below 75% relative humidity, open systems can offer high capacity inaddition to having lower energy needs. Therefore, having the ability totake in outside air and control the degree of open vs. closed willenable greater capacity control flexibility with outside temperature.

In an alternative embodiment an adjustable semi to full closed loophumidification-dehumidification solution concentrating system enablesgreater capacity control independent of external environmentalconditions. In the closed loop system saturated air circulates throughthe humidification and dehumidification zones through an adjoiningconduit or duct, which may be insulated. Circulation of the saturatedair stream prevents heat loss to atmosphere and enables operation at anelevated temperature. In cold climates, closed loop systems operating atan elevated internal temperature will have higher capacity than an opensystem operating at the colder external temperature. Insulating theprocess will further reduce heat losses, which if small can be replacedby supplementary compressor or available heat power.

Referring to FIG. 7 there is shown an adjustable closed loop solutionconcentrating system 301, which consists of three sub-systems:

-   -   Solution concentrating circuit: removes water from the system        via humidification zone 320 subsequently concentrating solution,        such as saltwater 305, in tank 304;    -   Carrier gas circuit: circulates a gas 330 through insulated duct        395 in a closed loop for subsequent humidification in        humidification zone 320 and dehumidification in dehumidification        zone 360. The gas 330 is herein referenced to air but could        include nitrogen, helium, methane or other gases that can be        consecutively humidified and dehumidified; noted that certain        carrier gases such as helium will provide capacity per unit        volume benefits due to their increases ability to hold moisture        per unit gas volume;    -   Heat pump circuit: captures heat from warm moist air 329 exiting        from humidification zone 320 and upgrades it to heat the salt        solution 305 in heat pump condenser 311;

The saltwater concentrating circuit accepts make-up saltwater 302 froman upstream process into bulk tank 304. Bulk tank 304 may include anoptional heater element 306, supplied with heat source 390, which warmsthe bulk salt solution 305 prior to pumping in order to reduce thelikelihood of precipitation in the downstream pipework. Heat source 390may include heat discharged from other processes, electric resistiveheating, or any other available heat source. Salt solution 305 exitsbulk tank 304 via an outlet. The outlet may be positioned at least 15 cmabove the tank base to prevent egress of solids that may haveaccumulated in the base of the tank 304. Main pump 308 pumps the saltsolution 305 through the heat pump condenser 311 where heat istransferred from condensing heat pump refrigerant thereby heating saltsolution 305. An optional downstream supplementary heat exchanger 310may be employed with external heat source 390. The supplementary heatexchanger 310 powered with external heat source 390 reduces heat pumpcompressor 374 load and capacity. One or more supplementary heatexchanger 310 may be added to the system depending on the availabilityand cost of heat source 390 in comparison to the cost of compressorcapacity and said compressor prime mover load.

The objective of heat exchanger 310 and heat pump condenser 311 is towarm the salt solution temperature to approximately 5 deg C. or greaterabove the wet bulb temperature of the air 330 entering thehumidification zone 320. The now warmed salt solution 305 enters thesalt solution distribution header 322, and passes through media 324 inhumidification zone 320 that promotes heat and mass transfer from waterto air. Exemplar media 324 includes, but is not limited to, typicalcooling tower splash fill or film fill packing known to those skilled inthe art. The salt solution in humidification zone 320, which is warmerthan the wet bulb temperature of the air 330 entering humidificationzone 320, transfers latent heat and evaporates water to air as they bothpass through humidification zone 320. As evaporation occurs, saltsolution 305 is cooled and concentrated. The cooled and concentratedsalt solution is captured in saltwater collection basin 326 and returnedto bulk tank 304. Concentrated salt water exits the system via manifold317. An optional precipitant and sediment collection vessel (not shown)may be inserted between saltwater collection basin 326 and bulk tank304. Solids may be extracted from the optional precipitant and sedimentcollection vessel. The saltwater concentrating circuit process can becompleted on a continual basis or batch basis. In continuous mode,make-up saltwater 302 is added, concentrated, and extractedcontinuously. In batch mode, tank 304 is filled, concentrated, and thendischarged.

Referring now to the air circuit, there is provided an insulated duct395 with an open system inlet vent 391, a closed system inlet vent 392,an open system outlet vent 393 and a closed system return vent 394 whichallow for hybrid operation between a fully open and fully closed system.Positions of the vents 391, 392, 393, 394 to provide for fully open andfully closed systems are given in Table 2.

TABLE 2 Positioning of vents for fully open and fully closed systemsFully Open Fully Closed Vent Description System System 391 Open SystemInlet Vent Open Closed 392 Closed System Inlet Vent Closed Open 393 OpenSystem Outlet Vent Open Closed 394 Closed System Return Vent Closed Open

The decision whether to operate as an open system, closed system, orpartially closed system may depend on the outside air temperature,outside air relative humidity, and the design temperature for the fullyclosed system. At a set closed system elevated design temperature, thereexists a break even capacity where closed and open systems capacity arematched for a lower outside air temperature and relative humidity, asdescribed above with reference to FIGS. 5 and 6. Generally, if theoutside air is below the break even air temperature and humidity, aclosed system will provide higher capacity. If however the outside airis above the break even air temperature and humidity, an open systemwill offer increased capacity and lower input energy requirements.Capacity and energy input can be adjusted beneficially above the breakeven air temperature and humidity by throttling open the open systeminlet and outlet vents 391, 393 and throttling closed the closed systeminlet and return vents 392, 394. This will allow outside air to enter,which if above the break even air temperature and humidity, will enableincreased capacity. If the outside air is warmer than the closed systemdesign elevated temperature, highest capacity will be achieved in fullyopen system mode. Adjustment of vents 341, 342, 343, and 344 allows foroptimization of capacity and energy for external conditions between thebreak even air temperature and humidity and closed system designelevated temperature.

Warm moist air 329 exiting humidification zone 320 passes through anoptional demister 365 to remove any entrained saltwater droplets. Asingle or multiple fans can be used and placed at a variety of locationsin the air circuit. In FIG. 7, a first fan 325 is placed after thehumidification zone 320 and a second fan 364 after dehumidification zone360. Those skilled in the art of humidification media design can specifythe air flow rate and surface area required to achieve the desiredevaporation rate based on air and saltwater temperatures as well asinform on the expected air pressure drop through the humidification zone320. Those skilled in the art of air systems design can size andspecific the fan location such that the required air flow rate can beprocessed based on the combined pressure loss of the humidification zone320, demister 365, dehumidification zone 360, air duct 395 and any othercomponents. The entire air circuit may be insulated for use in coldclimates in order to prevent sensible heat loss to the surroundings.Changing the internal air pressure of the system may also changecapacity. For example when operating at less than atmospheric pressure,the vapour fraction of water in the gas will increase thereby increasingcapacity. In a fully closes system gases other than air can also beused, for example methane, helium, hydrogen, or nitrogen with differingheat capacities that will provided different thermal and capacityperformance. When processing highly impaired waters, such as thosecontaminated with hydrocarbons, the open system vents 391 and 393 alsoprovide a means to release non-condensable gases and intake fresh air.The non-condensable gases may be passed through an air scrubber, such asactivated carbon filters, to remove any hazardous or detrimentalchemicals.

Referring now to the heat pump circuit, heat pump evaporator 370extracts heat from the dehumidification zone 360 by evaporating arefrigerant inside the heat pump evaporator 370. Those skilled in theart of dehumidification heat pump evaporator design can specify theevaporator surface area, heat transfer and pressure drop at the air flowrate. Moisture will condense external to the heat pump evaporator 370 onthe cold evaporator surface. Condensed moisture, which may be freshwater 383, is collected in basin 367 and sent out of the process foranother use. A heat pump compressor 374 compresses vaporized refrigerantexiting heat pump evaporator 370 to a sufficient pressure that enablesrefrigerant condensation in the heat pump condenser 311 at a temperaturegreater than the desired saltwater exit temperature from heat pumpcondenser 311. Liquid refrigerant at the elevated pressure exits thecondenser 311 and passes through a refrigerant expansion valve 378,which lowers the pressure to enable low temperature evaporation in theheat pump evaporator 370 and cooling of its external surface. Adjustmentof the refrigerant expansion valve 378 will adjust the heat pumpevaporator 370 thermal load and operating temperature. In thisembodiment an expansion valve is shown, however, in alternativeembodiments any refrigerant expansion device, for example a capillarytube, may be used to lower the pressure of refrigerant before it entersthe evaporator 370. Optionally, a heat pump evaporator defrosting system(not shown) may be included to defrost the evaporator surface. Exemplardefrosting systems include hot gas defrost, hot water defrost, andelectric defrost among others. Known to those skilled in the art; anexemplar heat pump compressor 374 may include, but is not limited to, ascrew or scroll compressor. An exemplar heat pump condenser 311 mayinclude, but is not limited to, a titanium plate and frame condenser. Anexemplar heat pump evaporator 370 may include, but is not limited to,copper tube aluminum finned evaporator coils. An exemplar refrigerantexpansion valve 378, may include, but is not limited to, thermostaticexpansion valves controlled based on the temperature of refrigerantexiting the evaporator.

If an external hot and cold source is available, the heat pump circuitmay be removed. The hot source can beneficially provide heat via heatexchanger 390 and the cold source providing cooling fluid to a finnedtube heat exchanger, or equivalent, in the same location as heat pumpevaporator 370. Removing the heat pump will reduce the electrical powerrequirements, yet a sufficient heat and cold source should be available.

The system described may be suited for modular dispatch and operation.Modules (not shown) can be built for ready transport and dispatch, withthe module shell providing protection from the environment, structuralsupport and restraint, and enabling simplified transport and siteimplementation. Exemplar modular dispatch could include constructing thehumidification and dehumidification zone into a standard ISO insulatedrefrigerated shipping container, with the refrigeration unit removed.Successive humidification and dehumidification zones with vents could bebuilt into a single 40 foot standard container. The humidification anddehumidification zone container could be mounted on top of anothersimilar module containing the saltwater pumps, tanks, electrical andcontrols infrastructure, and optional heat pump machinery, supplementaryheat exchanger, salt settling vessel, solids extraction system and thelike.

Saltwater concentrating systems concentrate a bulk salt solution byremoving water. As water is removed, the salt solution reachessaturation and solids can be formed in a collection cone tank. In analternative embodiment, solids, or a slurry of water and solids, areextracted using a motorized cooled auger. An auger cooling circuitlowers the temperature of the mixture being extracted which increasesits density to improve dewatering, and reduces the solubility ofdissolved salt to increase particle size; the combination of bothimprove salt extraction. The auger is angled to convey solid, such assalt at an incline with the auger exit opening at a higher level thanthe level of the solution in the collection cone tank. Materials ofconstruction such as polyethylene, polypropylene, or PTFE may bebeneficially used for their smooth surfaces and reduced likelihood ofsalt adhesion. An optional precipitation promoter unit or similar devicemay encourage salt precipitation in desired locations.

Referring to FIG. 8, there is shown a saltwater concentrating system 401with salt extractor apparatus, which consists of three sub-systems:

-   -   Saltwater concentrating circuit: removes water from the system        via evaporative tower 420 and produces solid or near solid salt        in collection cone tank 430;    -   Auger assembly: removes solids using auger 441;    -   Optional refrigeration circuit: withdraws heat from auger        cooling circuit using coolant heat exchanger 463 and upgrades        the heat using heat pump compressor 465 to preheat bulk solution        405 in condensing heat exchanger 467, or rejects the heat to        atmosphere.

In the exemplar saltwater concentrating circuit, bulk tank 404 receivessaltwater from saltwater source 402 that requires concentrating andvolume reduction. Saltwater from saltwater source 402 may include, butis not limited to, desalination plant brine or waste water from anindustrial process. Bulk tank 404 may include an optional heater element406, supplied with heat source 490, which warms the salt solution 405prior to pumping, in order to reduce the likelihood of precipitation inthe downstream pipework. Heat source 490 could include heat dischargedfrom other processes, electric resistive heating, or any other availableheat source. Salt solution 405 exits bulk tank 404 via an outlet. Theoutlet may be positioned at least 15 cm above the tank base to preventegress of solids that may have accumulated in the base of the tank 404.Bulk tank pump 408 pumps the salt solution 405 to evaporative tower 420that concentrates salt solution 405. The concentrated salt solution iscaptured in saltwater collection basin 426 and passes into collectioncone tank 430. If the concentrated salt solution reaches saturation dueto the removal of water, solid salt will precipitate. Heavier saltparticles fall to the base of collection cone tank 430 while the lowerdensity and less saturated solution rises and exits through conduit 436to return to bulk tank 404. The system is designed for temperaturestratification and hydraulics such that salt precipitates in the cooler,less turbulent, base of collection cone tank 430 while saltprecipitation is prevented in the warmer bulk tank 404. This is achievedby distributing the flow entering the cone tank 430 away from andpreventing downward thrust into the sedimentation zone. Thrust plates ordistributors (not shown) that prevent disturbance of salt at the base ofthe collection cone tank 430 can be employed. The saltwaterconcentrating circuit may operate on a continuous or batch basis. Undercontinuous operation, make-up salt water 402 is added, concentrated, andextracted continuously. In batch mode, tank 404 is filled, concentrated,and then discharged.

Referring now to the auger assembly, precipitated salt from the base ofcollection cone tank 430 passes into auger collection conduit 431 bygravity. If needed for matters of maintenance, collection cone tank 430and auger collection conduit 431 can be purged into collection bin 437by opening auger collection conduit purge valve 433. Purging ofcollection cone tank 430 and auger collection conduit 431 may berequired in the event of routine cleaning or to clear a blockageresulting from excessive scaling. Auger 441 is placed at an incline suchthat the blades at the lowest point of said auger 441 are within thecavity of auger collection conduit 431 and in contact with theprecipitated salts in said auger collection conduit 431. Auger 441 isdriven by auger motor 442 and rotates within auger housing 443 and augercollection conduit 431. Auger 441 conveys precipitated salts out ofauger collection conduit 431 and upwards through auger housing 443 toexit auger housing 443 at auger housing opening 445, then down augerhousing lip 447 and into salt disposal tank 449. Auger housing opening445 is located vertically higher than the level of the solution incollection cone tank 430 to prevent liquid in collection cone tank 430from exiting through auger housing 443. The speed, torque, and frequencyof operation of the auger motor 442 and the angle of auger 441 may beselected depending on the particle size, viscosity, rate ofprecipitation, and critical angle of repose of the mixture beingconveyed. Experiments have shown that the auger salt extraction rateincreases considerably when solids in the cone tank 430 are notdisturbed. It can therefore be beneficial to periodically stop inflowinto the cone tank 430 from evaporative tower 420. This will allowsolids to settle undisturbed and assist extraction. It can also bebeneficial to include a diffuser (not shown) within cone tank 430 todirect flow away from the bottom settlement zone.

Materials of construction for the auger assembly such as polyethylene,polypropylene, or other low friction materials may be beneficially usedfor their smooth surfaces and reduced likelihood of salt adhesion inauger assembly components and pipework. The auger assembly operates atnear ambient temperature which beneficially enables the use of lowercost plastics as materials of construction instead of corrosionresistant steels. The mechanical extraction of the auger assemblynegates the need for a slurry pump or downstream solids-liquidsseparating unit.

The auger assembly may also include an auger cooling circuit. Augercoolant tank 453 contains auger coolant 451. Exemplar coolants include,but are not limited to, fresh water, saltwater, ethylene glycol,propylene glycol, or other fluids with suitable thermal capacity,viscosity, and material compatibility with auger cooling circuitcomponents and pipework. Auger coolant pump 455 pumps inlet augercoolant 456 through auger coolant jacket 457 which surrounds augerhousing 443 using a spiral, parallel, or other arrangement. For example,auger coolant may flow inside the shaft of auger 441. Inlet augercoolant 456 beneficially lowers the temperature of the mixture beingextracted thus increasing its density and reducing solubility. Theincreased density beneficially reduces the height of the salt solutionslurry in the auger housing 443, providing an increased “dry zone”within the auger housing 443, which assists in solids de-watering. Thereduced solubility increases precipitation and particle size formationwithin the auger housing 443 and auger collection conduit 431. As aresult, the cooled auger assembly enables more reliable salt extraction.Inlet auger coolant 456 is warmed as it passes through auger coolantjacket 457. Warm outlet auger coolant 458 is returned to auger coolanttank 453.

Referring now to the refrigeration circuit 461, heat from auger coolant451 is extracted by heat exchanger 463 lowering the temperature of saidinlet auger coolant 456. Refrigeration circuit 461 contains arefrigerant which is expanded by expansion device 469 to evaporate at atemperature lower than the temperature of the inlet auger coolant 456plus an additional margin to allow for heat transfer resistance.Refrigeration compressor 465 compresses the refrigerant gas to asufficient pressure that will enable condensation of the refrigerant incondensing heat exchanger 467 at a temperature greater than the saltsolution 405 entering the condensing heat exchanger 467. This results incondensation of the refrigerant inside the condenser heat exchanger 467,transferring the refrigerant's latent heat of condensation to heat thesalt solution 405. This beneficially results in heat from outlet augercoolant 458 being upgraded to a higher temperature and recycled to heatsalt solution 405 before the salt solution enters evaporative tower 420.The pressure of refrigerant gas is reduced by passing the gas throughexpansion device 469 before it enters heat exchanger 463. Alternatively,heat extracted from auger coolant 451 may be directed to a heatexchanger (not shown) built into bulk tank 404 or to atmosphere (notshown). Alternatively and not shown, a thermo-electric chiller may beused in place of the refrigeration system heat exchanger 463, therebyremoving the need for refrigeration compressor 465 and expansion device469 described above. Thermo-electric chillers are known to those skilledin the art and built from dis-similar metals to provide a cooling effectthrough passage of electric current. Heat from the thermo-electricchiller may be optionally discharged to the environment or to thesaltwater through a heat exchange at a similar location to condensingheat exchanger 467.

The auger assembly may optionally include an electrically drivenprecipitation promoter unit 471 that induces dissolved salt toprecipitate into larger crystals thereby increasing the efficiency ofsalt extraction. Precipitation promoter unit 471 is connected to a powersupply 473 and attached to auger collection conduit 431 or otherlocations where increased precipitation is desirable. Exemplarprecipitation promoter units 471 may include, but are not limited to,solenoid-induced molecular agitation devices employing a solenoid coilcarrying an oscillating electric field and wrapped around the pipe inwhich increasing precipitation is desired.

The embodiment described above with reference to FIG. 8 describes theauger assembly in use with a exemplar salt concentrating circuit. Inalternative embodiments (not shown) the auger assembly may be used forcollecting and harvesting solids participated from solution with anysolution concentrating systems, such as the solution concentrationsystems shown in FIGS. 1 and 11-13.

Components that make-up a humidification driven saltwater concentratingsystem can develop scale with time, which will hamper performance. Hotfreshwater is an effective cleaning agent for many scaling compounds.However, hot freshwater may be scarce in some regions. Additionally,adding freshwater to the system is counterproductive given the purposeof the saltwater concentrating system which is to concentrate a saltsolution, therefore the amount of freshwater being added should beminimized.

In an alternative embodiment, the saltwater concentrating systemincludes an automated clean-in-place system to reliably clean componentsof the system. Process conditions are measured and interpreted todetermine when a cleaning is required. A wash solution, which could befreshwater, is heated and used to wash humidification zone media,commonly known as fill or packing, by spraying the scaled media withwarm wash solution at a low flow and moderate pressure. Wash solution isalso used to clean the saltwater pump, heat exchanger and other“in-pipe” components collectively defined as pipework. Sensors and logicare included to determine when cleaning is required. A control systemand actuated valves are included to minimize human intervention duringcleaning such that the system can run unattended and reliably;beneficially de-scaling itself when required.

Referring to FIGS. 9, 11 and 12 there is shown a humidification drivensaltwater concentrating system 501, 701, 801 with automatedclean-in-place system, which consists of two key operating modes:

-   -   1. Salt water concentrating mode    -   2. Cleaning mode

Actuated valves are included to swap between operations of (1) saltwater concentrating mode, and (2) cleaning mode. The saltwaterconcentrating mode is described first. Bulk tank 504, 704, 804 containssalt solution 505, 705, 805 received from saltwater source 502, 702, 802that requires concentrating and volume reduction. Salt solutions mayinclude but are not limited to desalination plant brine or waste waterfrom an industrial process. Bulk tank 504 may have an optional bulk tankheater 506 drawing heat from heat source 590. Bulk tank heater 506 heatsthe salt solution 505 to reduce the risk of precipitation in bulk tankpump 508. Exemplar heat sources 590 include: electric heat, reject heatfrom another process, or other suitable heat sources. Salt solution 505,705, 805 from bulk tank 504, 704, 804 exits through a normally open bulktank outlet actuated valve 512, 712, 812 and is pumped by bulk tank pump508, 708, 808 to heat exchanger 510, 710, 810 while passing throughpressure sensor 503 a, 703 a, 803 a; flow sensor 503 b, 703 b, 803 b;and conductivity sensor 503 c, 703 c, 803 c; collectively “sensors” 503,703, 803. One of each pressure sensor 503 a, 703 a, 803 a; flow sensor503 b, 703 b, 803 b; and conductivity sensor 503 c, 703 c, 803 c; areshown; however, they may be optionally removed or additional sensors maybe employed as specified by the designer. For example, temperaturesensors (not shown) could be added on the inlet and outlet of heatexchanger 510, 710, 810.

Heat exchanger 510, 710, 810 is provided with heat source 590, 790, 890that heats the saltwater to above the wet bulb temperature of the air550, 750, 850 passing through the humidification device 520, 720, 820.In the embodiment shown in FIG. 12, there is also a heat pump condenser811 in the solution flow path, which works in conjunction with heatexchanger 810 to heat the salt solution 805 before it enters thehumidification device 820. The now warmed salt solution 505, 705, 805passes through normally open humidification device actuated valve 509,709, 809 bypassing normally closed cleaning tank return actuated valve586, 786, 886 and bulk tank return actuated valve 535, 735, 835. Thesalt solution enters the salt solution distribution header 522, 722, 822and passes through humidification zone media 524, 724, 824 in directcontact with air 550, 750, 850. Air 550, 750, 850 passes throughhumidification zone media 524, 724, 824 under action of fan 525, 725,825. Humidification zone media 524, 724, 824 promotes heat and masstransfer between the saltwater and air, effecting evaporation of waterto air. Exemplar humidification zone media 524, 724, 824 may include,but are not limited to, cooling tower splash fill or film fill packingknown to those skilled in the art. The humidification zone media 524,724, 824 may be constructed from corrosion and scale resistant materialssuch as polyvinyl chloride, polypropylene or polyethylene. In theembodiment shown in FIG. 9, the cooled and concentrated salt solutionexits the humidification device 520 and is returned to bulk tank 504 viaconduit 540. In the embodiments shown in FIGS. 11 and 12 the cooled anconcentrated salt solution exits the humidification device 720, 820 andis returned to cone shaped bulk tank 704, 804 where salts may beprecipitated and collected as described below.

During normal operation, scale may develop on various salt waterconcentrating system components. In the cleaning mode operation, twocleaning modes may be utilized as follows:

1. Humidification zone cleaning mode

2. Pipework cleaning mode

These cleaning modes can be initiated based on pre-determined times orby sensing performance degradation and initiating cleaning only whenrequired. Scaling of system components will degrade performance.Cleaning will restore performance if the sealants can be removed by thecleaning solution.

The extent of scaling, and resulting need for cleaning, can be sensed asoutlined herein. Scaling of humidification zone media 524, 724, 824 canbe sensed by either increased fan 525, 725, 825 load measured by acurrent transducer on the fan motor power feed (not shown) or throughincreased differential air pressure measurement across the inlet andoutlet of the humidification zone media 524, 724, 824 measured by an airdifferential pressure sensor (not shown). An increase of either fanmotor current or air differential pressure will indicate humidificationzone media 524, 724, 824 scaling/clogging at which time thehumidification zone cleaning mode can be initiated.

Scaling of the bulk tank pump 508, 708, 808 and heat exchanger 510, 710,810 can be sensed by decreased flow at a set pressure for a fixed speedpump, or increased pump current draw for at a set flow rate or pressure.Scaling of heat exchanger 510, 710, 810 and heat pump condenser 811could also be sensed through degradation of heat transfer efficiency.Heat transfer efficiency degradation can be determined by a decrease inheat transfer coefficient, which can be deduced from temperature andflow measurement on the inlet and outlet of the heat exchanger 510, 710,810 and heat source 590, 790, 890; a method known to those skilled inthe art of heat exchangers. A decreased heat transfer coefficientindicates heat exchanger scaling. Indication of scaling of the bulk tankpump 508, 708, 808, heat exchanger 510, 710, 810, or heat pump condenser811, as determined by the measurements described, can be used toinitiate the pipework cleaning mode.

Pre-set cleaning times, or performance based process measurements asdescribed above can be used to initiate the cleaning modes. Prior toinitiating cleaning operation, the saltwater concentration mode ishalted by stopping bulk tank pump 508, 708, 808 and closing bulk tankoutlet actuated valve 512, 712, 812. The cleaning operations outlinedbelow can be extended or repeated as required to restore performance ofthe concentrating system 501, 701, 801.

The humidification zone cleaning mode cleans humidification zone media524, 724, 824. This mode is beneficially run first since cleaningsolution 585, 785, 885 will be less saline and therefore more efficientat cleaning humidification zone media 524, 724, 824. In the embodimentshown in FIG. 9, cleaning solution source 583 is input to cleaningsolution tank 580 to provide cleaning solution 585. In the embodimentsshown in FIGS. 11 and 12, condensed water vapour 766, 866 produced bydehumidifying device 760, 860 is directed to cleaning solution tank 780,880 to provide cleaning solution 785, 885 as described below in moredetail. In an alternative embodiment (not shown) a mixture of condensedwater vapour from the dehumidifying device and cleaning solution from anexternal source may be used to provide the clean solution. Cleaningsolution could be freshwater, saltwater, or a pre-determined mixtureoptionally including anti-scalants for the scaling species present aswould be known to those skilled in the art. For example, dilute citricacid may be used to de-scale calcium carbonate, whereas a basic solutionmay be used to de-scale silica scaling. Generally a freshwater cleaningsolution is preferred given the lack of chemical inputs and itsincreased solubility for scaled matter over saltwater. Cleaning solution585, 785, 885 in cleaning solution tank 580, 780, 880 is optionallyheated by cleaning solution tank heater 581, 781, 881 to a particulartemperature set point required to dissolve the scaled matter, but belowthe temperature compatibility limits of the materials used in thecomponents of the system. For example, cleaning solution 585, 785, 885may be heated to about 45 to 55 deg C. to increase solubility of scaledcomponents but remain within the temperature limits of exemplarpolyvinyl chloride materials. Cleaning solution tank heater 581, 781,881 draws heat from cleaning solution tank heat source 590, 790, 890.Exemplar cleaning solution tank heat sources 590, 790, 890 include, butare not limited to, electric heat; reject heat from other processes; orother heat sources available. Cleaning solution 585, 785, 885 fromcleaning solution tank 580, 780, 880 is pumped by cleaning solution pump553, 753, 853, along conduit 555, 755, 855, to spray nozzles 588, 788,888 directed at humidification zone media 524, 724, 824. The embodimentsshown allows the cleaning solution exiting humidification zone media524, 724, 824 to enter bulk tank 504, 704, 804 as opposed to returningto cleaning solution tank 580, 780, 880. This ensures that freshcleaning solution is always used to clean humidification zone media 524,724, 824, however in alternative embodiments other arrangements arepossible. Cleaning solution pressure and flow are matched to spraynozzle 588, 788, 888 design, which may be based on a low flow at a highpressure in order to minimize water addition to the solutionconcentrating system but maximize abrasive action through pressure.Exemplar pressures and flows may be up to 600 kPa and 1 liter per minuteper nozzle. Bulk tank return actuated valve 535 should be closed toprevent back-flow of cleaning solution to the saltwater concentratingcircuit.

The pipework cleaning mode may consist of the two operation modes asfollows:

-   -   a. Pipework closed loop cleaning mode: warm cleaning solution is        circulated through the pipework for a set period of time, for        example ten minutes, to allow for sufficient de-scaling; the        cleaning solution will be salinated with time;    -   b. Pipework cleaning solution discharge mode: the now spent and        salinated cleaning solution is drained from cleaning solution        tank 580, 780, 880;

The pipework closed loop cleaning mode cleans bulk tank pump 508, 708,808 sensors 503, 703, 803, heat exchanger 510, 710, 810 and heat pumpcondenser 811. This mode is beneficially run after the humidificationzone cleaning mode since cleaning solution 585, 785, 885 will besalinated during the pipework closed loop cleaning operation describedbelow. Nevertheless, the pipework cleaning mode can be run at any timeas required by either a pre-set timer, operator intervention, or bycontrol system decisions based on the sensed need for pipeworkde-scaling.

In pipework closed loop cleaning mode (a) bulk tank outlet actuatedvalve 512, 712, 812 is closed. Cleaning solution 585, 785, 885 is drawnfrom cleaning solution tank 580, 780, 880 through the open cleaning tankoutlet actuated valve 582, 782, 882, pumped by bulk tank pump 508, 708,808, past sensors 503, 703, 803, through heat exchanger 510, 710, 819,and heat pump condenser 811 and then returned to cleaning tank 580, 780,880 through the open cleaning tank return actuated valve 586, 786, 886.Over the duration of the pipework closed loop cleaning mode operation,cleaning solution 585, 785, 885 becomes increasingly saline.

Once a preset pipework closed loop cleaning mode time is reached, thepipework cleaning solution discharge mode (b) is initiated. The pipeworkcleaning solution discharge mode (b) is similar to pipework closed loopcleaning mode (a) with the exception that cleaning tank return actuatedvalve 586, 786, 886 is closed and bulk tank return actuated valve 535,735, 835 is opened. Pipework cleaning solution discharge mode (b) iscontinued until cleaning solution 585, 785, 885 in cleaning solutiontank 580, 780, 880 is substantially drained to bulk tank 504, 704, 804removing the salinated cleaning solution. The solution concentratingcircuit can then process the waste cleaning solution. Alternatively, thecleaning solution tank 580, 780, 880 may be drained to an external wastecollection system. Cleaning solution tank 580, 780, 880 may now berefilled with cleaning solution source 583 and/or condensed water vapour766, 866 and any of the cleaning modes repeated as required. Table 3below summarizes actuated valve operating position for each operatingmode.

TABLE 3 Operation positions for actuated valves for system operatingmodes Actuated Valve Bulk tank Humidification Bulk tank Cleaning tankCleaning tank Operation outlet actuated device actuated return actuatedoutlet actuated return actuated Mode valve 512, 712, 812 valve 509, 709,809 valve 535, 735, 835 valve 582, 782, 882 valve 586, 786, 886Saltwater Open Open Closed Closed Closed concentrating mode Cleaningmode: N/A N/A Closed N/A N/A humidification zone Cleaning mode: ClosedClosed Closed Open Open pipework closed loop Cleaning mode: ClosedClosed Open Open Closed pipework solution discharge

Additional cleaning modes which may be operated in the cleaning mode ofoperation include system flush mode and slug wash mode. System flushmode is activated at system shutdown in order to flush the pump 508,708, 808 and pipework and prevent crystallization in pump 508, 708, 808and pipework during standstill. Slug wash mode is activated at increasedpump loads to provide a low volume de-scaling freshwater slug in orderto clean the pump impeller and pipework. In system flush mode: cleaningtank outlet actuated valve 582, 782, 882 and cleaning tank returnactuated valve 586, 786, 886 are opened; bulk tank outlet actuated valve512, 712, 812 and humidification device actuated valve 509, 709, 809 areclosed; and pump 508, 708, 808 is activated for a set time (exemplar 60seconds) to flush the salt solution 505, 705, 805 from the pump 508,708, 808 and pipework prior to shut-down. In slug wash mode: cleaningtank outlet actuated valve 582, 782, 882 is opened and bulk tank outletactuated valve 512, 712, 812 immediately closed; a time delay is userset (exemplar 10 seconds); then bulk tank outlet actuated valve 512,712, 812 is opened and cleaning tank outlet actuated valve 582, 782, 882immediately closed.

The salt water concentrating system 701, 801 shown in FIGS. 11 and 12,have addition sub-systems:

-   -   Solids collection circuit: solids precipitated in cone shaped        bulk tank 704, 804 and collected using collection device (not        shown);    -   Condensed water production circuit: condenses water from warm        moist air 729, 829 leaving humidifying device 720, 820 using        dehumidifier 770, 870.

The salt water concentrating system 801 shown in FIG. 12, also has theaddition sub-system:

-   -   Heat pump circuit 872: captures heat from warm moist air 829        exiting from humidifying device 820 and upgrades it to heat the        salt solution 805 in heat pump condenser 811.

In the solids collection circuit, the cooled, concentrated salt solutionpasses into smooth bottomed collection basin 726, 826, which may have asmall retained volume to minimize heat loss of the retained solution toatmosphere, and then passes into the cone shaped bulk tank 704, 804. Adeflection plate (not shown) may be mounted under, but a distance from,the salt solution inlet into bulk tank 704, 804. The deflection platebeneficially prevents disturbance of the salt collecting in the base ofthe cone shaped bulk tank 704, 804. If the salt solution reachessaturation due to the removal of water and cooling, salts will form.Heavier salt particles fall to the base while the lower density and lesssaturated solution rises and exits via the outlet through action of pump708, 808 and re-circulates through the solution concentrating circuit.The system is designed for temperature stratification and hydraulicssuch that salts form in the cooler, stiller, base of cone shaped bulktank 704, 804.

Precipitated salts collecting in the bottom of cone shaped bulk tank704, 804 pass into conduit 731, 831. The precipitated salts may becollected using an auger assembly as shown in FIG. 8, a filter belt asshown in FIG. 1 or some other means of collection. If needed for mattersof maintenance or for collection of salts, cone shaped bulk tank 704,804 and conduit 731, 831 can be purged into collection bin 737, 837 byopening purge valve 733, 833. Purging of cone shaped bulk tank 704, 804and conduit 731, 831 may be required in the event of routine cleaning orto clear a blockage resulting from excessive scaling.

The solids collection circuit may optionally include an electricallydriven precipitation promoter unit 771, 871 that induces dissolved saltto precipitate into larger crystals thereby increasing the efficiency ofsalt extraction. Precipitation promoter unit 771, 871 is connected to apower supply 773, 873 and attached to conduit 731, 871 or otherlocations where increased precipitation is desirable. Exemplarprecipitation promoter units 771, 871 may include, but are not limitedto, solenoid-induced molecular agitation devices employing a solenoidcoil carrying an oscillating electric field and wrapped around the pipein which increasing precipitation is desired.

In the condensed water production circuit, warm moist air exhaust 729,829 produced as a result of evaporation of water from salt solution 705,805 to air 750, 850 in the humidification device 720, 820, is passedthrough to dehumidifying device 760, 860 under action of an optional fan764, 864. Fan 764, 864 may be removed if fan 725, 825 is sufficientlysized to induce the required air flow.

In the embodiment shown in FIG. 11, the dehumidifying device 760includes a dehumidifier 770. Dehumidifier 770 may be an evaporator orany other device which condenses water from the warm moist air exhaust729, for example a condensing heat exchanger, such as aluminum finnedtubes or the like. Input dehumidifier fluid 745, which may be arefrigerant or other fluid such as water or coolant, enters thedehumidifier 770. The temperature of input fluid 745 is lower than thewet bulb temperature of the moist air exhaust 729 plus an additionalmargin to allow for heat transfer resistance. As a result, water vapourcondenses from the humidifying device moist air exhaust 729 in contactwith the external surface of the dehumidifier 770. As water vapourcondenses, the latent heat of condensation is transferred to the fluidinside the dehumidifier 770, such that output fluid 748 leaving thedehumidifier 770 is at a higher temperature than the temperature of theinput fluid 745. The heat from output fluid 748 may be used as a heatsource, such as heat source 790 or may be dumped before the fluid isrecycled back to the dehumidifier 770.

In the embodiment shown in FIG. 12, the dehumidifying device 860includes a heat pump refrigerant evaporator 870. Inside the heat pumprefrigerant evaporator 870 refrigerant evaporates at a temperature lowerthan the wet bulb temperature of the air plus an additional margin toallow for heat transfer resistance. As a result, water vapour condensesfrom the humidifying device moist air exhaust 829 in contact with theexternal surface of the heat pump refrigerant evaporator 870. As watervapour condenses, the latent heat of condensation is transferred to therefrigerant inside the heat pump refrigerant evaporator 870.

Refrigerant gas passes from the heat pump refrigerant evaporator 870 toheat pump compressor 874. Heat pump compressor 874 compresses therefrigerant gas to a sufficient pressure that will enable condensationof the refrigerant in the heat pump condenser 811 at a temperaturegreater than the salt solution 805 inside the heat pump condenser 811.This results in condensation of the refrigerant inside the tubes of theheat pump condenser 811, transferring the refrigerant's latent heat ofcondensation to heat the salt solution 805 before it enters thehumidifying device 820. Condensed liquid refrigerant passes through anexpansion device 878 which lowers the pressure from the high to the lowpressure side of the heat pump cycle allowing low pressure refrigerantto enter the evaporator. Beneficially, the net result is that the latentheat from the condensing exhaust moist air 829 in contact withrefrigerant evaporator 870 is upgraded to a higher temperature andrecycled to heat salt solution 805 before it enters the humidifyingdevice 820, thereby reducing or eliminating the system net heat inputrequired from heat source 890 in the main heat exchanger 810 while alsoproducing condensed water vapour 866 that may be put to a secondarybeneficial use.

Exemplar heat pump compressors include, but are not limited to, standardrefrigeration system piston or screw compressors sized to match the heatpumps' evaporator and condenser operating pressures and flow rates. Therefrigerant evaporator 870 is exposed to the moist air exhaust 829 whichis less corrosive than other heat transfer surfaces in the system thatare exposed to the salt solution 805, therefore, exemplar refrigerantevaporator 870 materials may be, copper, cupric-nickel, or titanium.Exemplar refrigerants include, but are not limited to, R410A or R134a.The heat pump condenser 811 is exposed to the corrosive salt solution805 and therefore should be designed for corrosion resistance. Exemplarheat pump condensers 811 include, but are not limited to, tube-in-tubepolyethylene heat exchangers or titanium plate and frame heatexchangers. An exemplar refrigerant expansion valve 378, may include,but is not limited to, thermostatic expansion valves controlled based onthe temperature of refrigerant exiting the evaporator. The heat pumpcircuit 872 may be cycled on or off based on the availability of heatfrom heat source 890, measured as the salt solution 805 temperatureafter valve 809.

To facilitate the heat pump circuit 872 shown in FIG. 12, an air duct(not shown) may be provided to circulate air 850 exiting thedehumidifying device 860 back into the humidifying device 820. Thedegree of open versus closed loop is adjusted by controllable inletlouver or vent 815 and outlet louver or vent 817. As described abovewith reference to the embodiment shown in FIG. 7, the duct operatingtemperature may be adjusted up or down by reducing or increasing moistair discharge by closing or opening the louvers respectively. This willenable control of the air duct temperature, thereby controlling thetemperature of the heat pump refrigerant evaporator 870. Controlling thetemperature of the heat pump evaporator 870 enables control of therefrigerant saturation temperature and refrigerant pressure differenceacross the heat pump compressor 874.

The heat pump condenser 811 and heat pump refrigerant evaporator 870 maybe operated at as close temperature as possible, within limits ofmaterial temperature compatibility and compressor allowable operatingrange. Beneficially this improves energy efficiency by maximizing thecoefficient of performance of the heat pump cycle. The minimum allowabletemperature difference between the heat pump condenser 811 and heat pumprefrigerant evaporator 870 results from the minimum allowable pressuredifference across the heat pump compressor 874 to prevent suction liquidslugs while maintaining tolerable mechanical loads on compressorcomponents. Operating at or near this minimum allowable temperaturedifference minimizes compressor power consumption per unit of waterevaporated and condensed by maximizing the coefficient of performance(COP) of the heat pump cycle. Maximizing the COP translates intominimizing the units of mechanical energy input to the compressor shaftto move one unit of heat energy from the heat pump refrigerantevaporator 870 to the heat pump condenser 811, with each unit of heatproportional to units of water evaporated and condensed.

It is beneficial to operate the heat pump compressor 874 at thecompressor manufacturer's minimum stated pressure difference across thecompressor, which will minimize the difference between the condenserrefrigerant saturation temperature and the evaporator refrigerantsaturation temperature. This way the compressor is kept withinmanufacturer specified limits of minimum pressure difference across themachine, thereby resulting in minimization of the temperature differencebetween the heat pump condenser 811 and heat pump refrigerant evaporator870, which translates into energy efficiency as discussed above.

Condensed water vapour 766, 866 is captured in basin 767, 867 and may beoutput from the plant by opening water output valve 714, 814 and closingclean-in-place input valve 738, 838. Alternatively, the condensed watervapour 766, 866 may be added to cleaning solution tank 780, 880 to makeup clean-in-place solution 785, 885 by closing water output valve 714,814 and opening clean-in-place input valve 738, 838. Recycling thecondensed water vapour 766, 866 back to clean-in-place tank 780, 880beneficially minimizes the amount of water that needs to be added to thesystem.

The dehumidifying device 760, 860 can include an optional demister 765,865 that entrains any water droplets carried over to prevent loss to theenvironment. In an alternative embodiment (not shown), the air flow maybe orientated in vertical rather than horizontal configuration. Also theair flow in humidifying device 720, 820 may be oriented horizontallywith vertical air flow in dehumidifying device 760, 860, providing thebenefit of additional demisting as condensed vapour droplets will tendto fall out of the air flow as it turns from a horizontal to a verticalpath. Optional humidification device inlet louvers 721, 821 direct airinto the humidification zone media 724, 824 and can be closed to preventsplashing of saltwater out of the humidification device air inlet whenthe fan 725, 825 is not on during cleaning.

The embodiments shown in FIGS. 2 and 12 utilize an airhumidification-dehumidification (HDH) effect to produce condensed waterand to transfer heat of condensation to the solution to be concentratedbefore it enters the humidification device. In an alternative embodimentfor concentrating saltwater solutions multiple airhumidification-dehumidification (HDH) effects may be utilized. When asinge HDH effect is utilized as described above with reference to FIGS.2 and 12, a heat pump evaporator placed downstream of the humidificationstage warm moist discharge air stream provides a heat exchange surfacecooler than the wet bulb temperature of the air stream, thereby enablingcondensation of moisture from the air on the outside of the evaporatortubes. Condensation of moisture produces freshwater and latent heat ofcondensation. The latent heat of condensation of the moisture istransferred to the heat pump refrigerant as it evaporates inside theevaporator tubes. The low pressure heat pump refrigerant gas is thencompressed in a compressor in order to upgrade its latent heat ofcondensation to a higher temperature. The high pressure refrigerant isdischarged to a condenser wherein the refrigerant condenses and releasesits heat of condensation at a higher temperature, heating the saltwaterbefore it enters the humidification stage.

High pressure liquid refrigerant is produced in the condenser and may beexpanded to a lower pressure through an expansion device, such as athermostatic expansion valve, electronically controlled expansion valve,or a capillary tube. The lower pressure refrigerant then re-enters theevaporator. The heat pump closed loop refrigerant cycle is completedwith the refrigerant evaporating in the evaporator tubes. In sum, theheat pump cycle captures the latent heat of the condensing moisture fromthe dehumidification stage and upgrades it to warm the saltwater beforeit enters the humidification stage.

As described above, fully closed air loop concentrators operate atsaturated air conditions, with a humidity ratio of 1. Humidity ratio isdefined as the mass of water vapour in a volume of air relative to thepotential mass of water vapour at fully saturated conditions. In a fullyclosed loop concentrator, the humidity ratio remains 1 as the air streampasses through the humidification and dehumidification stages. As theair stream is heated in the humidifier by the warm inlet saltwater itstemperature and ability to hold vapour increases. As the air stream iscooled in the dehumidification stage by the cooler refrigerant fluidinside the heat pump evaporator, the air's ability to hold vapourdecreases and it moisture condenses on the cooler tubes.

From a saltwater processing capacity standpoint, it is beneficial tooperate a closed loop heat pump driven solution concentrator at as hightemperature as possible. This is because warm air can hold more moistureper unit volume than cooler air, as described above. Inlet and outletair vents or louvers enable closed loop air duct temperature control. Ina fully closed and perfectly insulated air loop arrangement the heatpower input into the air loop (condenser heat power=evaporator heatpower+compressor power) exceeds heat extracted from the air loop(evaporator heat power). More specifically, the compressor heat power isnot discharged from the system and as a result the air loop temperaturerises. Inlet and outlet vents are regulated to exhaust warm air andintake cooler air in order to control air loop temperature, beneficiallyaiming for a higher temperature to increase capacity, or for the heatpump system's most efficient operating temperature. The inlet and outletvents also provide a discharge mechanism of any unwanted gases such ashydrocarbon vapours that could be present in the saltwater, optionallythrough media that absorbs the hydrocarbon vapours such as activatedcarbon. Alternatively, the inlet and outlet vents or louvers could beremoved and replaced with a heat exchanger that discharges air loop heatwithout exhausting air.

Through a series of models, experiments and prototypes the following wasdiscovered:

-   -   An approximate 15 deg C. temperature difference between the        temperature of the warm saltwater entering the humidifier and        the temperature of the heat pump refrigerant in the dehumidifier        stage is required for effective condensation of moisture. Higher        temperature differences result in increased freshwater        production capacity;    -   Most heat pump compressors known in the art are best operated        when the condenser refrigerant saturation temperature is 30        deg C. or higher than the evaporator refrigerant saturation        temperature. Some compressor manufacturers specify a minimum        saturation temperature difference; others specify a minimum        pressure difference. Regardless, the specified difference of at        least 30 deg C. ensures that the low pressure refrigerant gas        entering the compressor suction does not include liquid        refrigerant slugs, which could damage the compressor;    -   The heat pump compressor 30 deg C. minimum temperature        difference stated above reduces energy efficiency since, the        heat pump cycle must operate at the optimal 30 deg C. minimum        temperature difference, however only a 15 deg C. minimum        temperature difference is actually required.

In order to overcome these shortcomings, while also beneficiallyincreasing saltwater concentrating capacity for the same size heat pumpsystem, multiple air humidification-dehumidification (HDH) effects maybe utilized. In this embodiment, the top temperature heat source isprovided by a heat pump condenser and the bottom temperature heat sinkis provided by the heat pump evaporator.

With reference to FIGS. 10 and 13, there is shown a solutionconcentrating plant 601, 901, using multiple air HDH effects whichconsists of four sub-systems:

-   -   1. First HDH effect saltwater concentrating circuit: including        first effect tank 604, 904, first effect pump 608, 908, and        first effect humidifier 620 a, 920 a;    -   2. Second HDH effect saltwater concentrating circuit: including        second effect tank 694, 994, second effect pump 696, 996, and        second effect humidifier 620 b, 920 b; second effect saltwater        692, 992 being lower in temperature than first effect saltwater        605, 905;    -   3. Heat pump circuit: captures heat from second effect        dehumidification stage heat pump evaporator 670, 970 and        upgrades it to heat the first effect saltwater 605, 905 in heat        pump condenser 611, 911;    -   4. Optional clean-in-place circuit: periodically de-scales and        cleans pumps 608, 908, 696, 996, heat pump condenser 611, 911,        first effect radiator 640, 940, and evaporative tower packing        624 a, 924 a, 624 b, 924 b.

The saltwater concentrating circuit accepts make-up saltwater 602, 902 afrom an upstream process into first effect tank 604, 904 afteroptionally being pre-heated by respective optional first and secondeffect condensed freshwater heat exchangers 607, 907 and 663, 963. Firsteffect tank 604, 904 may include an optional heater element 606, 906supplied by heat source 690, 990, which warms the bulk salt solution605, 905 prior to pumping. The optional heater element 606, 906beneficially reduces the likelihood of precipitation in downstreamprocess pipework. First effect salt solution 605, 905 exits bulk tank604, 904 via an outlet and passes through a normally open first effecttank actuated valve 612, 912. The optional clean-in-place first effecttank valve 682, 982 is normally closed. In one embodiment as shown inFIG. 13, the first effect salt solution 905 passes through pressuresensor 903 a, flow sensor 903 b, and conductivity sensor 903 c,collectively “sensors” 903. One of each pressure sensor 903 a, flowsensor 903 b, and conductivity sensor 903 c are shown; however, they maybe optionally removed or additional sensors may be employed as specifiedby the designer. For example, temperature sensors (not shown) could beadded on the inlet and outlet of heat exchanger 910. First effect pump608, 908 pumps the salt solution 605, 905 through the heat pumpcondenser 611, 911 where the salt solution 605, 905 is heated bycondensing high pressure refrigerant to a temperature roughly 1-10 degC. higher than the wet bulb temperature of the air entering the firsteffect humidifier 620 a, 920 a. Exemplar heat pump condenser 611, 911can include, but are not limited to titanium plate and frame units. Anadditional heat pump exchanger 910 heated by heat source 990 may beincluded in the first effect solution flow path as shown in FIG. 13 toprovide additional or alternative heating of first effect solution 905.

The warm first effect salt solution 605, 905 passes through the normallyopen first effect evaporative tower input valve 609, 909 and then entersthe first effect humidifier 620 a, 920 a via distribution header 622 a,922 a. The optional clean-in-place first effect recirculation valve 686,986 is normally closed. The warm first effect salt solution 605, 905drips through first effect humidification packing 624 a, 924 a in thefirst effect humidifier 620 a, 920 a, while fan 625 a, 925 a moves airthrough the packing 624 a, 924 a, promoting transfer of water to air.Water from the first effect salt solution 605, 905 evaporates to the airas the solution's temperature is higher than the wet bulb temperature ofthe air—a well known property of psychometrics. As a result, warm moistfirst effect air exhaust 629 a, 929 a is produced while the first effectsalt solution 605, 905 is cooled through loss of heat of vaporizationand concentrated through loss of water. The cooled, concentrated saltsolution collects in first effect collection basin 626 a, 926 a andreturns to the first effect tank 604, 904, which may include an optionalstrainer or filter (not shown) to remove any debris. The first effecthumidifier 620 a, 920 a is similar in construction to a cooling tower,which is known to those skilled in the art, but may be constructed fromnon-corrosive fibreglass shell, plastic packing materials such aspolyvinyl chloride or polyethylene, and alloyed steel or stainless steelhardware to prevent corrosion issues.

First effect evaporative tower moist air exhaust 629 a, 929 a passesthrough first effect dehumidification stage 660 a, 960 a. An optionalfan 664 a adjacent the dehumidification stage 660 a (as shown in FIG.10) may be included to induce the required air flow if required. Fan 664a may be removed if evaporated tower fan 625 a is sufficiently sized toinduce the required air flow. The first effect dehumidification stage660 a, 960 a includes the first effect radiator 640, 940. The firsteffect radiator 640, 940 may include optional finned tubes for enhancedheat transfer. Second effect salt water 692, 992 flows inside the tubesof the first effect radiator 640, 940. The second effect salt water 692,992 is cooler than the first effect moist air exhaust 629 a, 929 a,thereby enabling heat transfer, resulting in condensation of the firsteffect moist air exhaust 629 a, 929 a and transfer of latent heat ofcondensation of the moisture to heat the second effect saltwater 692,992. This condensation of moisture results in first effect freshwater699, 999, which is captured in first effect dehumidifier basin 667 a,967 a and delivered through first effect freshwater conduit 639, 939 tocondensed freshwater heat exchanger 607, 907. As shown in FIG. 13, thefirst effect dehumidifying device 960 a can include an optional demister965 a that entrains any water droplets carried over to prevent loss tothe environment.

In the embodiment shown in FIG. 13, the first effect freshwater 999 maybe output from the plant by closing first effect freshwaterclean-in-place input valve 938 a. Alternatively, the first effectfreshwater 999 may be added to cleaning solution tank 980 to make upclean-in-place solution 985 by opening first effect freshwaterclean-in-place input valve 938 a Recycling the first effect freshwater999 to clean-in-place tank 980 beneficially minimizes the amount ofwater that needs to be added to the system.

The second effect process arrangement is substantially similar to thefirst effect, with the exception that first effect radiator 640, 940 isreplaced with the second effect heat pump evaporator 670, 970. Thesecond effect saltwater 692, 992 is drawn from second effect tank 694,994 via an outlet and passes through normally open second effect tankactuated valve 613, 913. The outlet may be positioned to prevent egressof solids, such as a long horizontal pipe internal to the tank with topslots and a baffle above the slots to deflect solids from the pump inlet(not shown). An optional clean-in-place second effect tank valve 677,977 is normally closed.

Second effect pump 696, 996 pumps the second effect salt solution 692,992 through the first effect radiator 640, 940 inside the radiatortubes, where second effect salt solution 692, 992 is heated as describedabove. The warm second effect salt solution 692, 992 exiting firsteffect radiator 640, 940 passes along conduit 642, 942 to the secondeffect distribution header 622 b, 922 b through normally open actuatedvalve 689, 989. The optional clean-in-place second effect recirculationvalve 687, 987 is normally closed.

The warm second effect salt solution 692, 992 drips through thehumidification packing 624 b, 924 b in the second effect humidifier 620b, 920 b while second effect fan 625 b, 925 b moves air, promoting masstransfer of water to air. As a result, second effect warm moist airexhaust 629 b, 629 b is produced while the salt solution 692, 992 iscooled through loss of heat of vaporization and concentrated throughloss of water. The cooled, concentrated salt solution 692, 992 collectsin second effect collection basin 626 b, 926 b and is returned to thesecond effect tank 694, 994, which may include an optional strainer orfilter (not shown) to remove any debris.

In the embodiment shown in FIG. 10, salts 697 precipitated in secondeffect tank 694 may be collected using an auger assembly as shown inFIG. 8, a filter belt as shown in FIG. 1 or some other means ofcollection.

In the embodiment shown in FIG. 13, bulk tank 994 may have a bottomportion which is cone shaped to aid salt participation. A deflectionplate (not shown) may be mounted under, but a distance from, the saltsolution inlet into bulk tank 994. The deflection plate beneficiallyprevents disturbance of the salt collecting in the base of the coneshaped bulk tank 994. If the salt solution reaches saturation due to theremoval of water and cooling, salts will form. Heavier salt particlesfall to the base while the lower density and less saturated solution 992rises and exits via the outlet through action of pump 996 andre-circulates through the solution concentrating circuit. Make-upsaltwater 902 b from an upstream process may also be added into secondeffect tank 994 to make up second effect saltwater 992. The system isdesigned for temperature stratification and hydraulics such that saltsform in the cooler, stiller, base of cone shaped bulk tank 994.Precipitated salts collecting in the bottom of cone shaped bulk tank 994pass into conduit 931. The precipitated salts may be collected using anauger assembly as shown in FIG. 8, a filter belt as shown in FIG. 1 orsome other means of collection. If needed for matters of maintenance orfor collection of salts, collection cone shaped bulk tank 994 andconduit 931 can be purged into collection bin 937 by opening purge valve933. Purging of cone shaped bulk tank 994 and conduit 931 may berequired in the event of routine cleaning or to clear a blockageresulting from excessive scaling. Conduit 931 may include anelectrically driven precipitation promoter unit 971 that inducesdissolved salt to precipitate into larger crystals thereby increasingthe efficiency of salt extraction. Precipitation promoter unit 971 isconnected to a power supply 973 and attached to conduit 931 or otherlocations where increased precipitation is desirable. Exemplarprecipitation promoter units 971 may include, but are not limited to,solenoid-induced molecular agitation devices employing a solenoid coilcarrying an oscillating electric field and wrapped around the pipe inwhich increasing precipitation is desired. Once the first effectsaltwater concentrating circuit has been run for a set period of time,the first effect salt solution 905 in the first effect tank 904 willbecome concentrated. The concentrated first effect salt solution 905 maybe periodically drained from first effect bulk tank 904 into secondeffect bulk tank 994 by opening bulk tank transfer valve 961 and closingfirst effect humidifying device input valve 909. Transferring theconcentrated first effect salt solution 905 into the second effect bulktank 994 enables salts to be participated and collected from theconcentrated first effect salt solution as described above.

The second effect moist air exhaust 629 b, 929 b is passed over thesecond effect heat pump evaporator 670, 970 in the second effectdehumidification stage 660 b, 960 b. The heat pump evaporator 670, 970provides a heat exchange surface cooler than the wet bulb temperature ofthe moist air exhaust 629 b, 929 b air stream, leading to condensationof moisture from the air on the outside of the evaporator tubes.Condensation of moisture enables recovery of freshwater and the moistair's latent heat of condensation, which is transferred into the heatpump refrigerant as it evaporates inside the tubes of the heat pumpevaporator 670, 970. The low pressure heat pump refrigerant gas is thencompressed in heat pump compressor 674, 974 in order to upgrade itslatent heat of condensation to a higher temperature. The high pressurerefrigerant is discharged to condenser 611, 911 where the refrigerantcondenses and releases its heat of condensation at a higher temperature;thereby heating the first effect saltwater 605, 905 in the condenser611, 911 before it enters the first effect humidifier 620 a, 920 a. Highpressure liquid refrigerant is produced in the condenser 611, 911 andthen expanded to a lower pressure by passing through an expansion device678, 978. The low pressure refrigerant then re-enters the second effectevaporator 670, 970 and evaporates, capturing the latent heat of thecondensing moisture in the second effect dehumidification stage 660 b,960 b. The second effect dehumidification stage 660 b, 960 b producessecond effect freshwater 698, 998, which is captured in second effectdehumidifier basin 667 b, 967 b and delivered through second effectfreshwater conduit 669, 969 to condensed freshwater heat exchanger 663,963. As shown in FIG. 13, the dehumidification stage 960 b may includean optional demister 965 b that entrains any water droplets to preventcarry over.

In the embodiment of FIG. 13, the second effect freshwater 998 may beoutput from the plant by closing second effect freshwater clean-in-placeinput valve 938 b. Alternatively, the second effect freshwater 998 maybe added to cleaning solution tank 980 to make up clean-in-placesolution 985 by opening second effect freshwater clean-in-place inputvalve 938 b. Recycling the second effect freshwater 998 toclean-in-place tank 980 beneficially minimizes the amount of water thatneeds to be added to the system.

The first and second HDH effect systems include optional open-closedloop air ducts 695 a, 995 a and 695 b, 995 b respectively forrecirculation of air 950 a, 950 b. Increasing the first effect fan 625a, 925 a speed and pump 608, 908 flow rate will lower the temperaturedifference between the first and second effect. The higher first effectpump flow rate will lower the temperature difference between the firsteffect saltwater entering and exiting the first effect humidifier 620 a,920 a. Increasing fan speed will increase mass flow of air, leading towarmer exhaust air from first effect humidifier 620 a, 920 a, resultingin warmer second effect saltwater entering conduit 642, 942 on its wayto second effect distribution header 622 b, 922 b. As a result, thetemperature difference between the effects and under which the heat pumpmust be operated can be increased or decreased respectively bydecreasing or increasing fan speed and pump flow rate to a respectivenarrowing or widening of the temperature difference between effects.

The degree of open versus closed loop is adjusted by controllable inletlouver or vent 615 a, 915 a, 615 b, 915 b and outlet louver or vent 617a, 917 a, 617 b, 917 b. As described above with reference to theembodiment shown in FIG. 7, the duct operating temperature may also beadjusted up or down by reducing or increasing moist air discharge byclosing or opening the louvers respectively. This will enable coarsecontrol of first and second effect air duct temperature to achieve anoperating temperature, after which fan and pump speed control may beused to finely tune duct temperature, with the combination of bothcontrol means enabling control of the temperature of the first effectradiator 640, 940 and second effect heat pump evaporator 670, 970.Controlling the temperature of the first effect radiator 640, 940controls the temperature of the heat pump condenser 611, 911, whichcombined with control of the temperature of the second effect heat pumpevaporator 670, 970, enables control of the refrigerant saturationtemperature and refrigerant pressure difference across the heat pumpcompressor 674, 974.

As described above, compressor manufacturers will specify a minimumrefrigerant saturation temperature difference or pressure differenceacross the compressor in order to protect the compressor from damagingliquid refrigerant slugs. From an energy efficiency standpoint, it'spreferable to operate the compressor at as low pressure difference asthe process and compressor allows. This increases the coefficient ofperformance (COP) of the heat pump cycle. COP for heat pumps is theratio of heat power discharged in the condenser to the compressor power,a well know performance parameter known to those skilled in the art ofheat pump and refrigeration cycles. By controlling and reducing thetemperature difference between the first and second effect as describedabove, the operator can minimize compressor differential pressure butmaintain it above the manufacturer specified minimum. Therefore, theoperator can minimize compressor power, maximize COP, and therebymaximize the energy efficiency of the two effect heat pump drivenconcentrating system.

The heat pump condenser 611, 911 and heat pump refrigerant evaporator670, 970 may be operated at as close temperature as possible, withinlimits of material temperature compatibility and compressor allowableoperating range. Beneficially this improves energy efficiency bymaximizing the coefficient of performance of the heat pump cycle. Theminimum allowable temperature difference between the heat pump condenser611, 911 and heat pump refrigerant evaporator 670, 970 results from theminimum allowable pressure difference across the heat pump compressor674, 974 to prevent suction liquid slugs while maintaining tolerablemechanical loads on compressor components. Operating at or near thisminimum allowable temperature difference minimizes compressor powerconsumption per unit of water evaporated and condensed by maximizing thecoefficient of performance (COP) of the heat pump cycle. Maximizing theCOP translates into minimizing the units of mechanical energy input tothe compressor shaft to move one unit of heat energy from the heat pumprefrigerant evaporator 670, 970 to the heat pump condenser 611, 911,with each unit of heat proportional to units of water evaporated andcondensed.

It is beneficial to operate the heat pump compressor 674, 974 at thecompressor manufacturer's minimum stated pressure difference across thecompressor, which will minimize the difference between the condenserrefrigerant saturation temperature and the evaporator refrigerantsaturation temperature. This way the compressor is kept withinmanufacturer specified limits of minimum pressure difference across themachine, thereby resulting in minimization of the temperature differencebetween the heat pump condenser 611, 911 and heat pump refrigerantevaporator 670, 970, which translates into energy efficiency asdiscussed above.

The optional clean-in-place system periodically de-scales the pumps,heat exchangers, and evaporative tower packing. Hot freshwater, in therange of 45 deg C. may be used as clean-in-place solution.Clean-in-place freshwater supply 683 may be supplied externally (asshown in FIG. 10) or could be provided by diverting one or both of firsteffect freshwater 999 and second effect freshwater 998 to clean-in-placetank 980 (as shown in FIG. 13 and described above). The clean-in-placesystem periodically circulates clean-in-place solution 685, 985 throughpumps 608, 908 and 696, 996, condenser 611, 911, heat exchanger 910, andradiator 640, 940 in order to de-scale them. It also spraysclean-in-place solution on packing 624 a, 924 a, 624 b, 924 b of botheffects in order to de-scale the packing. The clean-in-place solution685, 985 may be heated with element 681, 981 in tank 680, 980 via heatsupply 690, 990. The clean-in-place solution 685, 985 may have acid,base, or anti-scalants added to reduce scaling, depending on thecomposition of the salt water. If for example the salt water is high insilica, pH can be increased to encourage de-scaling, while if the saltwater is high in carbonates, pH can be reduced to encourage de-scaling.Periodic exemplar initiation of the clean-in-place system may be basedon:

-   -   1. A timer set to past operational needs    -   2. Increase pump load or vibration    -   3. Reduced heat transfer in the condenser 611, 911 or radiator        640, 940 as measured relative to decreased temperature        differential    -   4. Increased evaporative tower fan 625 a, 925 a, 625 b, 925 b        load indicating packing scaling

Clean-in-place modes can be broadly categorized into the four categoriesas given in Tables 4 and 5 below which provide operation of theclean-in-place modes for the embodiments shown in FIGS. 10 and 13respectively. Prior to activating the specified clean-in-place mode,clean-in-place tank 680, 980 should be sufficiently full to complete themode and the clean-in-place solution 685, 985 heated to a predeterminedset point temperature to enhance cleaning effectiveness.

TABLE 4 Clean-in-place modes of operation for FIG. 10 Clean-in-placeMode First HDH Effect System Second HDH Effect System System flush:Activate 1. Open valves: 682, 686 1. Open valves: 677, 687 at systemshutdown in 2. Close valves: 612, 609 2. Close valves: 613, 689 order toflush pump 3. Activate pump 608 for set 3. Activate pump 696 for set andpipework and time (exemplar 60 sec) to time (exemplar 60 sec) to preventcrystallization flush salt solution from flush salt solution from inpump and pipework pipework prior to shut-down pipework prior toshut-down during standstill Slug wash: Activate at 1. Open valve: 682 1.Open valve: 677 increased pump loads 2. Immediately close valve: 2.Immediately close valve: to provide a low 612 613 volume de-scaling 3.Time delay user set: 3. Time delay user set: freshwater slug in orderexemplar 10 sec exemplar 10 sec to clean the pump 4. Open valve: 612 4.Open valve: 613 impeller and pipework 5. Immediately close valve: 5.Immediately close valve: 682 677 Pipework clean: 1. Open valves: 682,686 1. Open valves: 677, 687 activate after repeated 2. Close valves:612, 609 2. Close valves: 613, 689 slug washes or 3. Activate pump 608for set 3. Activate pump 696 for set measurement of heat time (exemplar20 mins) to time (exemplar 20 mins) to exchange heat transfer wash pump608, pipework, wash pump 696, pipework, deterioration indicating andcondenser 611 and radiator 640 scaling Drain tank 680, optionally intoDrain tank 680, optionally into tank 605 by opening valve 609 tank 694by opening valve 689 and closing valve 686 while and closing valve 687while running pump 608 until tank running pump 696 until tank 680reaches low level 680 reaches low level Packing clean: 1. Open valve:691 1. Open valve: 684 activate at increased 2. Close valve: 684 2.Close valve: 691 fan load or packing air 3. Activate pump 653 for set 3.Activate pump 653 for set pressure difference time (exemplar 60 sec) totime (exemplar 60 sec) to indicating packing direct wash solution 685 todirect wash solution 685 to scaling spray nozzles 688a to wash spraynozzles 688b to wash packing 624a packing 624b

TABLE 5 Clean-in-place modes of operation for FIG. 13 Clean-in-placeMode First HDH Effect System Second HDH Effect System System flush:Activate 1. Open valve: 982, 909 1. Open valves: 977, 989 at systemshutdown in 2. Close valve: 912, 986 2. Close valves: 913, 987, 935order to flush pump 3. Activate pump 908 for set 3. Activate pump 996for set and pipework and time (exemplar 60 sec) to flush time (exemplar60 sec) to flush prevent crystallization salt solution from pipeworksalt solution from pipework in pump and pipework prior to shut-downprior to shut-down during standstill Slug wash: Activate at 1. Openvalve: 982 1. Open valve: 977 increased pump loads 2. Immediately closevalve: 912 2. Immediately close valve: 913 to provide a low 3. Timedelay user set: exemplar 3. Time delay user set: exemplar volumede-scaling 10 sec 10 sec freshwater slug in order 4. Open valve: 912 4.Open valve: 913 to clean the pump 5. Immediately close valve: 5.Immediately close valve: impeller and pipework 982 977 Pipeworkclean: 1. Open valves: 982, 986 1. Open valves: 977, 987 activate afterrepeated 2. Close valves: 912, 909 2. Close valves: 913, 989, 935 slugwashes or 3. Activate pump 908 for set 3. Activate pump 996 for setmeasurement of heat time (exemplar 20 mins) to time (exemplar 20 mins)to exchange heat transfer wash pump 908, pipework, heat wash pump 996,radiator 940, deterioration indicating exchanger 910, and condenser andpipework scaling 911 Drain tank 980, optionally into Drain tank 980,optionally into tank 994 by opening valve 935 tank 905 by opening valve909 and closing valve 987 while and closing valve 986 while running pump996 until tank running pump 908 until tank 980 reaches low level 980reaches low level Packing clean: 1. Open valve: 991 1. Open valve: 984activate at increased 2. Close valve: 984 2. Close valve: 991 fan loador packing air 3. Activate pump 953 for set 3. Activate pump 953 for setpressure difference time (exemplar 60 sec) to direct time (exemplar 60sec) to direct indicating packing wash solution 985 along conduit washsolution 985 along conduit scaling 955 to spray nozzles 988a to 955 tospray nozzles 988b to wash packing 924a wash packing 924b

In the embodiment shown in FIG. 13, clean-in-place solution 985 whichhas become salinated following pipework clean mode may be drained intosecond effect tank 994 by opening valve 935 and closing valve 987 whilerunning second effect pump 996 until tank 980 reaches low level. Thisbeneficially allows the salinated clean-in-place solution 985 to bedrained to the second effect tank 994 without passing through andcontaminating either the first effect or second effect humidificationpacking 924 a, 924 b.

The first and second effect evaporative tower packing cleaning spraynozzles 688 a, 988 a, 688 b, 988 b direct clean-in-place solution 685,985, which may be warm low salinity water, at a high pressure and lowflow rate at the packing surface 624 a, 924 a, 624 b, 924 b to removeattached scaled. A minimal amount of water is beneficially added to thesystem. Make-up clean-in-place solution 683, which may be freshwater dueto its increase solubility action, but could also be saltwater, can beadded to the clean-in-place tank 680 based on an actuated valve or floatvalve. Actuated valves could be automatically actuated in accordancewith the above mentioned initiation examples using common air orelectric valve actuation systems in accordance with a programmable logiccontroller (not shown). Optional first effect humidification deviceinlet louvers 621 a, 921 a and second effect humidification device inletlouvers 621 b, 921 b direct air into the first effect packing 624 a, 924a and second effect packing 624 b, 924 b respectively. The inlet louvers621 a, 921 a, 621 b, 921 b can be closed to prevent splashing ofsaltwater out of the humidification device air inlet when the fan 625 a,925 a, 625 b, 925 b are not on during cleaning.

The embodiment described herein with reference to FIGS. 10 and 13 usestwo HOH effect driven solution concentrating system, however inalternative embodiments (not shown) the system may encompass more thantwo effects where:

-   -   The heat pump evaporator is located in the lowest temperature        effect's dehumidifying device;    -   The heat pump condenser heats the saltwater for the highest        temperature effect's humidification stage.

In an alternative embodiment, the capacity per unit footprint of theabove described system may be increased by using helium rather than airin the air ducts. This would of course entail fully closed and sealedloop operation to prevent egress of helium and ingress of atmosphericair. A heat exchanger between the helium duct and ambient would berequired to remove the heat power of the compressor and enable heliumloop temperature control.

In an alternative embodiment (not shown), the closed loop air ducts 995a and 995 b of FIG. 13 may be joined into a single adjustable closedloop air duct spanning two effects such that air flows through firsteffect humidification packing 924 a under action of fan 925 a, acrossfirst effect radiator 940, then in series to the second effecthumidification packing 924 b under action of fan 925 b and across secondeffect evaporator 970 before being returned in a closed loop to firsteffect humidifier packing 924 a. In this embodiment, the singleadjustable closed loop air duct has an air outlet louver and air inletlouver positioned between the first effect radiator 940 and secondeffect humidification packing 924 b to allow for control of thetemperature of the air passing into the second effect humidificationpacking 924 b, such that the air has a wet bulb temperature lower thanthe second effect salt solution entering the second effect distributionheader 922 b. In this embodiment, heat pump compressor power consumptionwill be higher than the embodiment shown in FIG. 13 however only oneduct system is required.

In an alternative embodiment (not shown), which uses a first and secondeffect saltwater concentrating circuit as shown in FIG. 13, theevaporator 970, compressor 974, condenser 911 and expansion device 978may be removed and a heat source, such as a heat exchanger 910, may beincluded in the system to heat the first salt solution before it enterthe first humidification device 920 a. The second saltwaterconcentrating circuit may include a humidification device and the warmmoist air produced in the humidification device may exhaust toatmosphere. Alternatively, the second saltwater concentrating circuitmay include a humidification-dehumidification device combination forconcentrating the second salt solution. When ahumidification-dehumidification device combination is used in the secondcircuit, a condensing heat exchanger, such as a radiator may be used inthe second effect dehumidification device instead of the evaporator 970.The radiator has a cooling fluid flowing internal to the radiator tubesso that there is condensation of water vapour from the second effectwarm moist air exhaust passing over the radiator. Heat of condensationis transferred to the cooling fluid in the radiator and the heatedcooling fluid may be cooled by a separate means such as a conventionalcooling tower or finned air cooler.

A multiple effect system can be built to beneficially recycle the heatof condensation and reduce the net thermal input. For example, a threeeffect system would reduce the net thermal input to roughly 220 kWh/m3since the input heat can be recycled three times. Additional effectswill reduce the net thermal input further; however the number of effectsis limited by the temperature difference between the hot sourcetemperature and heat rejection temperature, and the temperaturedifference required internally for each effect. As an example, a firsteffect may be designed for a temperature difference of 20 degreesbetween the warm first effect saltwater input to the first effecthumidification stage and the subsequent second effect saltwater exitingthe first effect condensing heat exchanger. If the system's first effectwarm saltwater temperature is 80 deg C. and final rejection occurs at 20deg C., three effects are possible.

In a multiple effect system, saltwater to be concentrated in adownstream effect is heated by passing the saltwater through adehumidification device of the next upstream effect before the saltwaterenters the humidification device of the downstream effect. Thedownstream effect operates at temperature lower than the upstreameffect. Saltwater passing into a first effect humidification device of amultiple effect system may be heated to a temperature above the wet bulbtemperature of gas flowing through the first effect humidificationdevice using a heat exchanger or the like. The heat source may be anexternal heat source, for example medium grade waste heat reject from anindustrial process or solar thermal. Alternatively or additionally, theheat source may be provided by a heat recovery circuit including anevaporator, compressor, condenser and expansion device as described withreference to FIG. 13, where the evaporator is positioned in thedehumidification device of the final effect.

Saltwater circulating through a humidification device of a second effectof the multiple effect system is heated to a temperature above the wetbulb temperature of gas flowing through the second effect humidificationdevice, by passing the saltwater through a condensing heat exchanger inthe dehumidification device of the first effect. Water vapour from thewarm moist exhaust gas passing over the condensing heat exchanger in thefirst effect dehumidification device condenses, and the heat ofcondensation is transferred to the saltwater. Saltwater circulatingthrough a humidification device of a third effect of the multiple effectsystem is heated to a temperature above the wet bulb temperature of gasflowing through the third effect humidification device, by passing thesaltwater through a condensing heat exchanger in the dehumidificationdevice of the second effect. Water vapour from the warm moist exhaustgas passing over the condensing heat exchanger in the second effectdehumidification device condenses, and the heat of condensation istransferred to the saltwater. The saltwater heating process is repeatedfor a fourth and subsequent effects if present.

The final effect in the multiple effect system operates in a mannersimilar to the upstream effects however the final effect does notrequire a dehumidification device and warm moist exhaust gas from thefinal effect humidification device may be exhausted to atmosphere.Alternatively, the final effect may include a dehumidification device.Heat produced in the final effect dehumidification device must berejected or recovered. Heat rejection may be provided by input ofcooling fluid into a condensing heat exchanger in the final effectdehumidification device to extract the final stage heat of condensation,heating the cooling fluid and rejecting heat from the process. Thecooling fluid may be cooled by means known to those skilled in the art,including but not limited to open source liquid cooling such as a waterbody, radiators rejecting heat to ambient air, and cooling towers. Heatrecovery may be provided by a heat recovery circuit including anevaporator, compressor, condenser and expansion device as described withreference to FIG. 13, where the evaporator is positioned in the finaleffect dehumidification device and heat from condensation of thecompressed refrigerant gas is transferred to the saltwater entering thefirst effect humidification device.

Saltwater may circulate through each of the multiple effects beingfurther concentrated as it passes through the humidification device ofeach effect. Valves may be used to transfer the circulating saltwaterfrom an upstream effect to a downstream effect. Each valve may bemodulated to transfer concentrated saltwater from the upstream effect tothe downstream effect at a mass flow rate equal to the differencebetween the input feed saltwater mass flow rate and the water lossevaporation mass flow rate in the humidification device of the upstreameffect. Alternatively, saltwater being concentrated in each effect maybe kept separate and may be circulated back to a bulk tank for eacheffect as shown in FIG. 13. If separate saltwater concentrating circuitsare used, a closable flow path (for example valve 961 in FIG. 13) may beprovided that links each circuit.

The multiple effect arrangement described above may have feed saltwaterinput to the first effect and concentrated solution circulated down tolower effects. This arrangement would be beneficial when the feedsaltwater is warm as may be the case for saltwater produced in oilprocesses. Alternatively, the feed saltwater may be input to the finaleffect's saltwater circuit. In this arrangement the saltwaterconcentrated in the final effect would be circulated to the nextupstream effect and so on until it is eventually discharged from thefirst effect. This arrangement may be beneficial when the feed saltwateris cool, as may be the case for reverse osmosis desalination plant brinedischarge.

Freshwater produced in the dehumidification devices of the multipleeffect system is collected and may be removed from the system orutilized as a clean-in-place solution as described above with referenceto FIG. 13. The freshwater produced in the first effect is warmer thansubsequent effects and heat exchangers may be used to exchange heatbetween the warm condensed freshwater from upper effects to preheat thesaltwater being fed into the system. This will beneficially reduce thenet thermal energy input requirement.

While particular embodiments have been described in the foregoing, it isto be understood that other embodiments are possible and are intended tobe included herein. It will be clear to any person skilled in the artthat modification of and adjustments to the foregoing embodiments, notshown, are possible.

The invention claimed is:
 1. A system for concentrating a solution comprising: a first solution concentrating circuit comprising: a first humidification device comprising a first humidification media; a first dehumidification device in gas flow communication with the first humidification device; a first solution flow path for flow of a first solution to be concentrated to the first humidification device; the first humidification media facilitating evaporation of liquid from the first solution to be concentrated to a first gas as the first solution to be concentrated passes through the first humidification media thereby concentrating the first solution and producing a first humidified gas; a second solution concentrating circuit comprising: a second solution container; a second humidification device comprising a second humidification media; a second solution flow path for flow of a second solution to be concentrated to the second humidification device; the second humidification media facilitating evaporation of liquid from the second solution to be concentrated to a second gas as the second solution to be concentrated passes through the second humidification media thereby concentrating the second solution and producing a second humidified gas; and wherein the first dehumidification device comprises a condensing heat exchanger in the second solution flow path such that the second solution to be concentrated passes internal the condensing heat exchanger and is heated by heat generated from condensation of vapour from the first humidified gas on the external surface of the condensing heat exchanger, the condensing heat exchanger heating the second solution to be concentrated before the second solution to be concentrated enters the second humidification device.
 2. The system of claim 1, further comprising a first duct connecting a first gas outlet from the first dehumidification device with a first gas inlet into the first humidification device.
 3. The system of claim 2, wherein the first duct comprises a first closable outlet vent for controlled release of the first dehumidified gas from the first duct as required and a first closable inlet vent for controlled input of external gas into the first duct as required.
 4. The system of claim 3, wherein the first duct further comprises a first internal closable return vent for controlled recirculation of the first dehumidified gas through the first duct as required and a first internal closable inlet vent for controlled introduction of the first dehumidified gas into the first humidification device as required.
 5. The system of claim 1, further comprising a second dehumidification device in gas flow communication with the second humidification device, such that the second humidified gas flows from the second humidification device to the second dehumidification device, wherein the second dehumidification device is operable to condense vapour from the second humidified gas.
 6. The system of claim 5, further comprising a heat recovery circuit comprising a heat recovery evaporator, a heat recovery compressor, a heat recovery condenser and a heat recovery expansion device, wherein the second dehumidification device comprises the heat recovery evaporator configured such that heat generated from condensation of vapour from the second humidified gas is transferred to a heat recovery refrigerant within the heat recovery evaporator to evaporate the heat recovery refrigerant, the heat recovery compressor is configured to compress the evaporated heat recovery refrigerant, the heat recovery condenser is configured to condense the compressed heat recovery refrigerant and transfer the heat of condensation of the heat recovery refrigerant to the first solution to be concentrated before the first solution to be concentrated enters the first humidification device, and the heat recovery expansion device is configured to expand the compressed heat recovery refrigerant before the heat recovery refrigerant enters the heat recovery evaporator.
 7. The system of claim 4, further comprising a second duct connecting a second gas outlet from the second dehumidification device with a second gas inlet into the second humidification device.
 8. The system of claim 7, wherein the second duct comprises a second closable outlet vent for controlled release of the second dehumidified gas from the second duct as required and a second closable inlet vent for controlled input of external gas into the second duct as required.
 9. The system of claim 8, wherein the second duct further comprises a second internal closable return vent for controlled recirculation of the second dehumidified gas through the second duct as required and a second internal closable inlet vent for controlled introduction of the second dehumidified gas into the second humidification device as required.
 10. The system of claim 1 further comprising a cleaning circuit comprising: a cleaning solution container for cleaning solution; a closable first outlet flow path fluidly connecting the cleaning solution container with the first solution flow path, for controllable flow of cleaning solution from the cleaning solution container through at least part of the first solution flow path; and a closable second outlet flow path fluidly connecting the cleaning solution container with the second solution flow path, for controllable flow of cleaning solution from the cleaning solution container through at least part of the second solution flow path.
 11. The system of claim 10, wherein the first and second outlet flow paths are closable by a one way valve.
 12. The system of claim 10, wherein the cleaning circuit further comprises a closable first return flow path fluidly connecting the first solution flow path with the cleaning solution container for return flow of cleaning solution to the cleaning solution container, and/or a closable second return flow path fluidly connecting the second solution flow path with the cleaning solution container for return flow of cleaning solution to the cleaning solution container.
 13. The system of claim 12, wherein the first return flow path and/or the second return flow path are closable by a one way valve.
 14. The system of claim 10, wherein the cleaning circuit further comprises a heater for heating the cleaning solution.
 15. The system of claim 10, further comprising one or more sensors for sensing process conditions that indicate a build up of solids in at least one of the first solution flow path or the second solution flow path to provide an indication that the cleaning circuit needs to be activated.
 16. The system of claim 1, further comprising one or more additional solution concentrating circuits positioned between the first and second solution concentrating circuits such that solution to be concentrated in an additional circuit is heated in a condensing heat exchanger of a dehumidification device of an upstream solution concentrating circuit before the solution to be concentrated enters a humidification device in the additional circuit.
 17. A system for concentrating a solution comprising: a humidification device comprising humidification media; a solution flow path for flow of a solution to be concentrated to the humidification device, the humidification media facilitating evaporation of liquid from the solution to be concentrated to gas as the solution to be concentrated passes through the humidification media thereby concentrating the solution; a dehumidification device in gas flow communication with the humidification device such that humidified gas flows from the humidification device to the dehumidification device, the dehumidification device operable to condense vapour from the humidified gas; a heat recovery circuit comprising a heat recovery evaporator, a heat recovery compressor, a heat recovery condenser, and heat recovery expansion device, wherein the dehumidification device comprises the heat recovery evaporator configured to transfer heat generated by condensing vapour from the humidified gas to a heat recovery refrigerant within the heat recovery evaporator such that the heat recovery refrigerant evaporates, the heat recovery compressor is configured to compress the evaporated heat recovery refrigerant, the heat recovery condenser is configured to condense the compressed heat recovery refrigerant and transfer the heat of condensation of the heat recovery refrigerant to the solution to be concentrated before the solution to be concentrated enters the humidification device, and the heat recovery expansion device is configured to expand the compressed heat recovery refrigerant before the heat recovery refrigerant enters the heat recovery evaporator.
 18. The system of claim 17, further comprising a duct connecting a gas outlet from the dehumidification device with a gas inlet into the humidification device.
 19. The system of claim 18, wherein the duct includes a closable outlet vent for controlled release of dehumidified gas from the duct as required and a closable inlet vent for controlled input of external gas into the duct as required.
 20. The system of claim 19, wherein the duct further comprises an internal closable return vent for controlled recirculation of the dehumidified gas through the duct as required and an internal closable inlet vent for controlled introduction of the dehumidified gas into the humidification device as required.
 21. The system of claim 17 further comprising a cleaning circuit comprising: a cleaning solution container for cleaning solution; and a closable outlet flow path fluidly connecting the cleaning solution container with the solution flow path, for controllable flow of cleaning solution from the cleaning solution container through at least part of the solution flow path.
 22. The system of claim 21, wherein the outlet flow path is closable by a one way valve.
 23. The system of claim 21, wherein the cleaning circuit further comprises a closable return flow path fluidly connecting the solution flow path with the cleaning solution container for return flow of cleaning solution to the cleaning solution container.
 24. The system of claim 23, wherein the return flow path is closable by a one way valve.
 25. The system of claim 21, wherein the cleaning circuit further comprises a heater for heating the cleaning solution.
 26. The system of claim 21, further comprising one or more sensors for sensing process conditions of the system that indicate a build up of solids in the solution flow path to provide an indication that the cleaning circuit needs to be activated.
 27. A system for concentrating a solution comprising: a humidification device comprising humidification media; a solution flow path for flow of a solution to be concentrated to the humidification device, the humidification media facilitating evaporation of liquid from the solution to be concentrated to gas as the solution to be concentrated passes through the humidification media thereby concentrating the solution; a dehumidification device in gas flow communication with the humidification device such that humidified gas flows from the humidification device to the dehumidification device, the dehumidification device operable to condense vapour from the humidified gas; and a duct connecting a gas outlet from the dehumidification device with a gas inlet into the humidification device, the duct comprising a closable outlet vent for controlled release of dehumidified gas from the duct as required and a closable inlet vent for controlled input of external gas into the duct as required.
 28. The system of claim 27, wherein the duct further comprises an internal closable return vent for controlled recirculation of the dehumidified gas through the duct as required and an internal closable inlet vent for controlled introduction of the dehumidified gas into the humidification device as required. 